Which File Extensions Carry Viruses? And Which Malware Changes Them?

Certain file extensions are notorious carriers of digital threats, often hiding under seemingly harmless facades. Here’s an exploration of file extensions that demand caution and vigilance.

Which File Extensions Carry Viruses?

While theoretically, any file can carry viruses, some extensions repeatedly appear in malicious activities. According to a study reported by Statista, Microsoft Windows .exe files are the most common malware file type worldwide, followed by .sh files for scripts. Notably, .html files frequently appear in email-related malware activities.

Let’s dive into file extensions often lurking at the heart of digitally disruptive attacks:

1. EXE: Executable files initiate programs or operations on your computer. This dual potential makes them particularly hazardous—like a two-faced coin. A simple rule? If you don’t trust the source 110%, keep that .exe at a safe distance.
2. DLL: Dynamic Link Libraries Though less frequently mentioned in virus discussions, .dll files can also be troublesome. They serve as libraries for executables to function but can be manipulated for malicious activities. Malware might slip a rogue DLL into your system, allowing legitimate processes to unknowingly trigger them.
3. BAT and CMD: Command Line Application Files Programmers use .bat (batch) and .cmd (command) files to automate tasks, but these files can house potent system-altering scripts. Execution might alter system settings or deploy hidden payloads without much trace for the average user. Always scrutinize unexplained batch or command files that appear in your email or downloads.
4. ZIP, RAR, and 7Z: Compressed Archives Big things in small packages hold true here. Compressed files like .zip, .rar, and .7z package multiple files—which unfortunately makes them perfect malware carriers. A Trojan might lurk in those seemingly innocent archives. Always scan these with your anti-malware tools before unzipping.
5. XLS, DOC, and PPT: Document Files with a Hidden Agenda Office documents like Excel (.xls), Word (.doc), and PowerPoint (.ppt) often come with macros. While handy for automation, macros can be exploited for malware—like a magician’s sleight of hand. Such macro viruses can launch malicious scripts as soon as you open a document.
6. PIF: The MS-DOS Era Trickster .PIF files, designed to give DOS programs execution instructions, seem harmless. But don’t be deceived. If these files contain executable code, Windows treats them like .exe files—executing troublesome code while wearing the disguise of digital nostalgia.
7. REG: Registry Manipulator The Windows Registry, akin to your system’s nervous system, is pivotal for functionality. A rogue .REG file can modify or obliterate key registry entries, replaced with junk data, akin to letting a stranger tamper with your car’s engine—proceed with extreme caution.
8. JS: The Script Everyone Loves to Hate JavaScript (.JS) enhances web interactivity but, outside the web browser’s safe sandbox environment, runs unrestricted, making them a potential malware breeding ground in unrestricted environments.
9. SH: Script for Shell Lovers Used in Unix-based systems, .sh files allow command execution within a shell, much like .bat or .cmd files in Windows. While Linux and macOS include some safeguards, certain configurations can leave systems exposed.
10. HTML attachments are the most exploited type of text file, with 23% found to be malicious. In fact, over 75% of all malicious files detected were HTML. While HTML files can serve legitimate purposes—like delivering newsletters or event invites that render correctly in email clients or web browsers—they’re also heavily abused by cybercriminals.

More Than Just A List

This list isn’t exhaustive. Files like PDFs have also presented vulnerabilities, making them potential risks if mishandled.

The common thread among these file types is their capacity to execute code or commands. This power makes them double-edged swords, providing functionality while potentially serving as Trojan horses for threats. The takeaway? Vigilance and skepticism are your best defenses. Always validate sources and steer clear from executing unknown files. Keep your security software updated. In the world of file extensions, ignorance isn’t bliss—it can be dangerous.

Which virus changes file extensions?

Ransomware is an especially insidious form of malware that drastically changes how victims can access their files. By encrypting data and attaching a new extension, ransomware serves both as a warning and a branding exercise. New extensions often include the ransomware strain’s name, such as “.locky,” “.crypt,” or “.wannacry,” instantly signaling to users that their files are inaccessible and encrypted.

These modified extensions have dual roles: they indicate danger and enable ransomware to readily identify which files have been altered for potential decryption, should the ransom be paid. This tactic introduces a psychological element of urgency and panic, highlighting the transformation of ordinary files into hostage data. The extension alteration is a deliberate strategy to make users acutely aware of the breach, thereby pressuring them to consider paying the ransom to reclaim their valuable data.