Beware! The 10 Most Dangerous File Types That Hackers Use to Hide Malware in 2026
Let's be honest: the thought of downloading a virus usually conjures up images of shady websites and suspicious-looking .exe files. However, the reality of modern cyberattacks is far more insidious. In 2026, your device is far more likely to be infected by a file you interact with every single day—a PDF invoice, a Word document, or even a harmless-looking image.
Cybersecurity experts at Kaspersky recently revealed that their systems detect an average of 500,000 malicious files every single day, a 7% increase from the previous year. The attackers aren't just writing new viruses; they are getting smarter at hiding them in plain sight. While the classic "Beware of EXE files" advice still holds true, today's threat landscape is much more complex.
We analyzed the latest threat reports from 2025 and 2026 to bring you the definitive guide to the file types most likely to contain viruses. Whether you use Windows, Mac, or Linux, understanding these threats is your first line of defense.
The Shifting Landscape of Malware Delivery
Before diving into the list, it's important to understand how these files reach you. According to a 2025 OpenText report, while email attachments remain a popular method, the majority of malware (53%) is now delivered via .zip archives, followed by HTML files and PDFs. Attackers are moving away from single executable files and toward containers that can bypass basic email scanning.
Furthermore, a NordVPN report analyzing attacks from 2024 to 2025 ranked Canada as the third most malware-infected country in the world, highlighting that this is a global issue affecting users in every region. The methods of delivery have also evolved significantly. Cybercriminals now employ sophisticated social engineering tactics, often impersonating trusted institutions like banks, government agencies, or well-known corporations. They meticulously research their targets through social media and other public sources to craft convincing lures. These lures might appear as urgent legal notices, enticing lottery winnings, or even romantic interests—all designed to lower the victim's guard and prompt them to open a malicious attachment without a second thought. With that context, let's look at the files you need to handle with care.
Part 1: The Classic Threats That Still Dominate
1. Executable Files (.exe, .msi, .dll, .appx)
As highlighted by the original article from Computer-WD, .exe files are the backbone of software on Windows, and consequently, a prime vehicle for viruses. However, the family of "executables" is larger than you think.
The Risk:
When you double-click an .exe, it runs code. If that code is malicious, your system is immediately compromised. This is because executable files have the highest level of access to your operating system's functions. They can read, write, modify, and delete files, install software, and even change core system settings without any additional prompts once granted initial execution.
2026 Update:
Attackers are now also heavily leveraging Microsoft Installer files (.msi, .appx) to distribute ransomware. Cloudflare recently expanded its file controls to block these specific installer types because they are often trusted by corporate systems but can contain hidden payloads. Even .dll (Dynamic Link Library) files, which are used by legitimate programs, can be "side-loaded" by malware to run malicious code from within a trusted application. This technique, known as DLL hijacking or sideloading, exploits the way Windows searches for necessary libraries, allowing malware to insert itself into the startup process of legitimate, trusted software.
Real-World Example:
In late 2025, a sophisticated ransomware campaign targeted manufacturing firms by distributing infected .msi installers disguised as updates for popular industrial control software. Because the files carried a valid digital signature stolen from a legitimate developer, they bypassed initial security checks and caused significant operational disruptions across three continents.
2. Compressed Archives (.zip, .rar, .7z)
Compressed files are the "gift boxes" of the malware world. You don't know what's inside until you open it. Their innocuous appearance and widespread use in business and personal communications make them a perfect delivery mechanism.
The Risk:
Archives can contain any other file type on this list. The OpenText report found that 53% of malware delivered via email now comes in the form of .zip files. Attackers love them because they compress malware to avoid detection and can even be password-protected, hiding the contents from security scanners. The password is typically provided in the email body, meaning automated security tools cannot peek inside to analyze the contents, forcing the user to become the final line of defense.
Why It Works:
A file named invoice_2026.zip is far more likely to be opened than a suspicious .exe. The psychology behind this is powerful. People expect invoices, receipts, and documents to arrive in compressed folders, especially in professional settings. This familiarity breeds contempt for the potential danger.
The Nested Archive Trick:
A particularly devious technique involves nested archives. A victim might receive a .zip file that contains another .rar file, which then contains a .js script. This multi-layered approach is designed specifically to evade email gateways that might only scan the outer layer or have timeouts preventing deep inspection.
3. PDF Files (.pdf)
PDFs are ubiquitous, used for everything from contracts to e-tickets. This universal trust makes them incredibly dangerous. They are the standard for document exchange across virtually every industry, from healthcare to finance to education.
The Risk:
A PDF can contain embedded JavaScript code that runs when the file is opened, or it can contain a malicious link. The JavaScript can be triggered automatically upon opening or when the user interacts with a specific element. This code can then exploit vulnerabilities in the PDF reader software itself to execute malware on the system.
A 2025 Barracuda Networks report found that 68% of malicious PDFs contain QR codes that lead to phishing sites—a tactic known as "quishing". Once you scan the code with your phone, you bypass the security of your computer entirely. This is particularly dangerous because mobile devices often have less stringent security protections than corporate laptops.
How QR Codes Are Used:
Attackers embed QR codes that appear legitimate, such as ones claiming to be for two-factor authentication setup, document verification, or payment processing. When scanned, they lead to high-fidelity phishing pages that steal credentials. Since the QR code is an image within the PDF, traditional text-based security filters often miss the malicious intent entirely.
Beyond QR Codes:
PDFs can also contain embedded forms that submit data to external servers, or they can exploit features like LaTeX or XFA (XML Forms Architecture) to execute commands on the host system. Even annotations and comments within a PDF can be weaponized to hide malicious links.
4. Microsoft Office Documents (.doc, .docx, .xls, .pptx)
Office files are a favorite among corporate spies and ransomware gangs. The deep integration of Microsoft Office into the daily workflow of businesses worldwide makes them an exceptionally effective attack vector.
The Risk:
The primary danger here is Macros. These are small scripts designed to automate tasks, but they can also be used to download and install malware. While modern versions of Office disable macros by default, attackers use social engineering to trick users into re-enabling them. The message might say, "This document was created in an older version of Office. Please enable editing and content to view it correctly."
New Tactic:
Attackers are now using OLE (Object Linking and Embedding) objects within documents to link to malicious files stored on remote servers, making them harder to detect. When the document is opened, it reaches out to the attacker's server to pull in the malicious payload dynamically, meaning the document itself may initially appear clean to scanners.
The Rise of Excel 4.0 Macros:
Cybersecurity researchers have noted a resurgence in the use of Excel 4.0 macros, an older macro language that predates VBA (Visual Basic for Applications). These macros are harder for security tools to parse and detect because they use a different structure and can execute directly without calling typical "malicious" functions. Attackers use them to run PowerShell commands or download next-stage payloads while flying under the radar.
OneNote Attacks:
In 2024 and continuing into 2026, Microsoft OneNote files have emerged as a significant threat. Attackers embed malicious files inside OneNote notebooks, often behind a large "Double-Click to View Document" overlay that actually executes a hidden script or executable.
5. Script Files (.js, .html, .vbs, .py)
Scripts are essentially text files containing instructions for a computer to execute. They are small, easy to obfuscate, and very powerful. Their simplicity belies their destructive potential.
The Risk:
An October 2025 phishing report noted a significant rise in the use of compressed RAR archives containing JavaScript (.js) files. When opened, these scripts can download the Remcos RAT (Remote Access Trojan), giving hackers full control over your PC. JavaScript, in particular, is dangerous because it can interface with Windows components via Windows Script Host, allowing it to execute commands, download files, and modify the registry.
HTML (.html):
You might not think of a webpage as a "virus," but the Barracuda Networks report also noted that 23% of HTML attachments are malicious. These files often contain obfuscated code that redirects you to a phishing site or triggers a drive-by download. The HTML file acts as a middleman, sometimes using meta-refresh tags or JavaScript to instantly forward the user to a malicious site without any visible interaction.
PowerShell (.ps1) and VBScript (.vbs):
These are native Windows scripting languages with deep system access. A single line of PowerShell can download and execute a payload from the internet. Attackers often encode these scripts in Base64 to hide the commands from simple text-based detection. VBScript, while deprecated in some Windows versions, is still widely used in attacks targeting older systems and can execute almost any system command.
The Fileless Aspect:
Script-based attacks often operate "filelessly." The script runs entirely in memory, never touching the hard drive. This allows it to bypass traditional antivirus software that scans files on disk. Once the script is finished running, there may be no trace left for forensic analysis.
Part 2: The Rising Threats You Must Know in 2026
6. Disk Image Files (.iso, .dmg, .img)
These files are digital copies of physical disks. They are commonly used to distribute software and operating systems. They function as virtual containers that, when opened, mount as a new drive on your computer.
The Risk:
On Windows, .iso files are frequently used to bypass security policies that block .exe files. A user might download an .iso, double-click it to "mount" it as a virtual drive, and then run the malware inside, thinking it's a legitimate installer. Because the operating system treats the mounted ISO as a new physical drive, files within it are often subjected to less stringent security checks than those downloaded directly.
On Macs, .dmg (Disk Image) files serve the same purpose and are increasingly being used to target macOS users. For years, Mac users enjoyed a sense of invincibility regarding malware, but that era is over. A malicious .dmg file can contain a trojanized version of a popular Mac app, and when installed, it can request extensive permissions (like accessibility or disk access) that grant it control over the entire system.
Why Bypassing Works:
Many email security gateways and web filters are configured to block .exe files. However, they often allow .iso and .dmg files because they are seen as data containers rather than executable code. Once the user mounts the disk image and double-clicks the file inside, the damage is done.
The Rise of .img and .vhd:
Attackers are also using .img (raw disk image) and .vhd (Virtual Hard Disk) files. These can be mounted in Windows without third-party software and contain entire file systems, allowing attackers to hide malware deep within folder structures.
7. HTML Files (.html, .htm)
While HTML is the language of the web, it's becoming a direct attack vector. It's the file type that builds the internet, but in the wrong hands, it builds convincing traps.
The Risk:
Attackers send HTML files as attachments that look like a login page for Microsoft or Google. When you open the file in your browser, it's a perfect replica of the real login page. Any credentials you enter are sent directly to the attacker. This method is harder for email filters to block than a simple link.
Phishing 2.0:
Modern malicious HTML files often include sophisticated code that detects whether they are being viewed in a sandbox or a real browser. If detection is triggered, they might display benign content (like a simple "page not found" error) to avoid analysis. Only when opened in a genuine user's browser do they redirect to the phishing page.
HTML Smuggling:
Another advanced technique is HTML smuggling. The malicious payload (like a JavaScript file or executable) is actually encoded within the HTML file itself. When the browser renders the HTML, a script runs that decodes and reassembles the malicious file directly on the user's machine. This process bypasses network-based security controls because the malicious content is never transmitted as a separate file; it's created locally by the browser.
8. Image Files (.jpg, .png, .svg)
This is the "wolf in sheep's clothing" of the list. While the original Computer-WD article mentions that images aren't completely safe, the threat has evolved dramatically. We've moved from theoretical vulnerabilities to real-world exploits.
The Risk:
Through a technique called steganography, attackers can hide malicious scripts or code within the pixels or metadata of an image file. When a vulnerable application loads the image, that code can be triggered. This works by slightly altering the color values of pixels in ways imperceptible to the human eye, allowing binary data (the malware) to be stored within the image.
Steganography in Practice:
Imagine a phishing email containing a single .jpg image attachment. The image looks like a corporate logo or a simple graphic. Hidden within the image data, however, is an encrypted script. When opened with a vulnerable image viewer or a program with an unpatched exploit, the script is extracted and executed. This method is notoriously difficult to detect because the image itself is not inherently malicious—it's just a carrier.
SVG (.svg):
This is a particularly dangerous image format because it is based on XML and can contain embedded JavaScript. An SVG image viewed in a browser can easily execute a malicious script. Since SVG files are vector-based and used everywhere from website icons to complex illustrations, the attack surface is enormous. A single malicious SVG uploaded to a company website could compromise every visitor.
Exploiting Image Parsers:
Even without steganography, image parsers (the code that reads image files) can have vulnerabilities. A specially crafted .png or .gif file can trigger a buffer overflow, allowing attackers to execute arbitrary code on the system. This was seen in various zero-day exploits targeting popular messaging apps that automatically render image previews.
9. Android Package Files (.apk)
With the majority of the world using mobile devices, malware is migrating. Our phones hold the keys to our digital lives: emails, banking apps, social media, and private photos.
The Risk:
.apk files are the installers for Android apps. While the Google Play Store has protections, downloading an .apk from a third-party website is a major risk. These files can contain spyware, banking trojans, or ransomware designed specifically for your phone.
Beyond the Play Store:
Attackers often promote malicious .apk files through social media ads, forum posts, or even direct messages. The apps might claim to offer premium features for free, such as a cracked version of a popular game or a modded streaming app. Once installed, they request extensive permissions that are completely unnecessary for their stated function—like a calculator app asking for access to your contacts and SMS messages.
Banking Trojans:
Mobile banking trojans are particularly sophisticated. They can overlay fake login screens on top of legitimate banking apps, capturing credentials as they are typed. Some can even intercept SMS messages, bypassing two-factor authentication codes sent via text. The 2025 NordVPN report highlighted a 200% increase in mobile banking trojans, directly correlating with the rise in mobile banking usage worldwide.
Sideloading Risks:
Even on iPhones, sideloading apps (installing from outside the official App Store) is becoming more common in some regions due to regulatory changes. This opens up iOS users to the same risks Android users have faced for years, as .ipa files (iOS app packages) can also be weaponized.
10. Shortcut Files (.lnk, .url)
You might think a shortcut is just a pointer to a real file, but in Windows, it can contain code. It's one of the most underestimated threats in the modern cybersecurity landscape.
The Risk:
Malicious .lnk files can be crafted to run a hidden command or PowerShell script when double-clicked. They often exploit the icon of a legitimate program (like a folder) to trick the user into clicking. When you double-click what appears to be a folder, you're actually executing a command that downloads and runs malware from the internet.
How LNK Attacks Work:
A .lnk file contains not just a target path but also icon information, hotkeys, and arguments. Attackers can set the target to something like cmd.exe /c powershell -EncodedCommand <base64>. The icon is set to look like a folder or document. When clicked, the command runs invisibly in the background while Windows tries to open the non-existent folder, often showing an error message to the user while the malware installs silently.
URL Files (.url):
Similarly, .url files are internet shortcuts. They can be crafted to point to local files or commands instead of web addresses. A .url file might look like it's pointing to a company website, but behind the scenes, it's configured to run an executable from a network share.
The Perfect Blend:
Attackers often combine .lnk files with other techniques. For example, a .zip archive might contain a folder icon that is actually a .lnk file. When the user double-clicks the "folder," the .lnk executes a script hidden in a companion file within the same archive, ensuring both files are present for the attack to succeed.
How to Protect Yourself from File-Based Threats in 2026
Knowing the dangerous file types is only half the battle. Knowledge without action is merely trivia. Here are actionable steps, informed by the latest cybersecurity strategies, to keep your data safe.
1. Adopt a Zero-Trust Mindset (Content Disarm and Reconstruction)
Traditional antivirus software tries to detect known malware, but it fails against new, never-before-seen "zero-day" threats. This detection-based model is inherently reactive—it only works after the threat has been identified and added to a database.
Security experts now recommend a strategy called Content Disarm and Reconstruction (CDR) .
How It Works:
Instead of just scanning a file, CDR assumes every file is guilty. It breaks the file down, removes all the potentially dangerous objects (scripts, embedded objects, macros, OLE links), and then rebuilds it into a clean, safe version. This ensures that even if a file contains a new virus, the dangerous parts are stripped away before you ever see it. The process is like taking a suspicious package, carefully unpacking it, removing anything that looks like an explosive, and then repackaging the safe contents for delivery.
Implementation:
Many modern email security gateways and advanced endpoint protection platforms now offer CDR capabilities. For businesses, this is becoming a necessity rather than a luxury. For individuals, choosing security software that includes behavior-based detection and CDR-like features provides an extra layer of defense.
2. Never Blindly Click: Verify the Source
Check the sender: Did you receive an unexpected invoice or voicemail from a sender you don't recognize? Treat it with extreme suspicion. Look at the email address carefully—often, attackers use domains that are one letter off from legitimate ones (e.g.,
@micros0ft.cominstead of@microsoft.com).Hover over links: Before clicking a link in a document or email, hover your mouse over it to see the actual destination URL. If the text says "Microsoft Security" but the link goes to
bit.ly/randomstringor a misspelled domain, do not click.Be QR-code wary: Never scan a QR code from an unsolicited email or letter. If you receive a physical letter with a QR code claiming to be from your bank, go to the bank's website directly rather than scanning the code.
Call to confirm: If you receive an urgent request from your CEO, a vendor, or a family member asking you to open an attached file, pick up the phone and call them directly to verify. Voice verification is the strongest defense against business email compromise.
3. Disable Macros and Show File Extensions
Office Macros: Keep Office macros disabled by default. If a document tells you to enable macros to view the content, close the file immediately—it is almost certainly a trap. No legitimate document requires you to enable dangerous scripting just to read text.
Show File Extensions: Windows hides file extensions by default. Enable "File name extensions" in File Explorer. This allows you to see if a file named
document.pdfis actuallydocument.pdf.exe. This simple visual check is one of the most effective ways to spot malicious files.Configure Windows to show hidden files: Many malware strains hide themselves by setting the "hidden" attribute. Configure your File Explorer to show hidden files and protected operating system files so you can see everything on your system.
4. Use Robust, Layered Security
Keep everything updated: Ensure your operating system, browser, and software are always patched. The Kaspersky report noted that vulnerabilities remain the most popular way for attackers to enter corporate networks. Enable automatic updates wherever possible.
Use strong passwords and MFA: The rise in "password stealers" (up 59% in 2025 according to NordVPN) means your password is likely to be stolen. Multi-Factor Authentication (MFA) ensures that a stolen password isn't enough to access your accounts. Use an authenticator app rather than SMS when possible.
Reputable Security Software: Use a comprehensive security suite from a trusted provider like Kaspersky, Bitdefender, or Malwarebytes, and ensure real-time scanning is always on. These suites now include web protection that can block malicious downloads before they reach your system.
Network-Level Protection: Consider using a DNS filtering service like Cloudflare's 1.1.1.2 or OpenDNS that blocks known malicious domains at the network level. This protects all devices on your home network, including IoT devices that cannot run antivirus software.
5. Practice Smart Backup Hygiene
Even with the best prevention, no system is 100% secure. Ransomware remains a dominant threat because it doesn't just infect files—it holds them hostage.
The 3-2-1 Backup Rule:
3 copies of your data (one primary and two backups)
2 different media types (e.g., external hard drive and cloud storage)
1 copy stored offsite (physically separated from your computer)
Immutable Backups:
Modern backup solutions offer "immutability," meaning once data is written, it cannot be changed or deleted for a set period. Even if ransomware encrypts your main system and connected drives, an immutable backup in the cloud remains safe and recoverable.
Test Your Backups:
Backups are useless if they don't work. Regularly test restoring files from your backup to ensure the process works and the data is intact.
The Future of File-Based Threats
As we look toward the remainder of 2026 and beyond, several trends are emerging that will shape the threat landscape.
AI-Generated Malware
Artificial intelligence is a double-edged sword. While defenders use AI to detect threats, attackers are using generative AI to create polymorphic malware that constantly changes its code to avoid signature-based detection. AI can also generate highly convincing phishing emails in perfect language, eliminating the grammatical errors that once gave them away.
Deepfake-Enabled Social Engineering
Imagine receiving a voicemail from your boss's voice, generated by AI, urgently asking you to open an attached file. This is already happening. Deepfake audio and video will be used to create incredibly convincing social engineering attacks that bypass traditional skepticism.
Supply Chain Attacks
Attackers are increasingly targeting software vendors and update mechanisms. By compromising a single trusted software provider, they can distribute malware to thousands or millions of users through automatic updates. This shifts the target from individual users to the developers they trust.
Cross-Platform Malware
Malware that can run on Windows, Mac, Linux, Android, and iOS from a single codebase is becoming more common. Written in languages like Rust or Go, these cross-platform threats can infect any device, making network segmentation more critical than ever.
Conclusion: Vigilance Is Your Ultimate Weapon
The golden age of ignoring file extensions is over. In 2026, the difference between a normal workday and a devastating data breach could be a single click on a malicious PDF or a seemingly harmless .zip file. The threat landscape has evolved from amateur hackers seeking notoriety to sophisticated criminal enterprises and state-sponsored actors with vast resources.
By understanding the tactics used by modern hackers and adopting a cautious, zero-trust approach to every file you download, you can stay one step ahead. Remember, the goal is not just to detect the threat, but to prevent it from ever running on your device.
Key Takeaways:
Be skeptical of every unexpected file, regardless of the sender or file type.
Enable visual defenses like showing file extensions and disabling macros.
Use layered security including updated software, reputable antivirus, and MFA.
Maintain offline backups to recover from ransomware attacks.
Stay informed about new threats by following reputable sources like Kaspersky, BleepingComputer, and The Hacker News.
Stay vigilant, keep your software updated, and always think before you click. The internet is a powerful tool, but it is also a minefield. Walk carefully, and you'll reach your destination safely.
Did you find this guide helpful? Share it with friends and family to help them stay safe online. For more in-depth cybersecurity insights, bookmark Computer-WD and check back regularly for updates.