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Dangerous File Extensions

Typical way how viruses, adware and malware get to the user computer is either via file downloaded from untrusted website, an attachment from untrusted e-mail or a malicious file received from messaging application. Dangerous file extensions are closely related to a subject of this website – binary files or more specifically binary executable files. When you download a binary executable file from the internet and launch it you pretty much give it full control of your computer. Malicious file can create copies of itself, plug itself into your e-mail, copy your personal data to the computer on the internet and do many more unauthorized actions. That is why it is important to know which files could be dangerous for your computer and why.

Below we list file extensions which are most frequently used to attack user computer. Most of them are binary executable files but we also listed several scripts and macros file extensions to make sure list is complete:

• EXE, COM, SCR – all these files are in executable file format. When you click on them after download they will launch as an application with full access to your computer. Thus, it is very important not to run files of this type unless they were downloaded from a trusted source.
• VBS, BAT, CMD – executable scripts. Files in these formats are text files containing commands for the computer. It is possible for an attacker to write such script files that they will copy themselves, steal user data and do other malicious actions on the user computer.
• APP – executable binary for Mac operating system. Similar to EXE files when executed it will have full control of computer it is running on. Do not run any APP files unless they were downloaded from a trusted source. Preferably don’t run downloaded APP files at all but instead download applications only from the Apple Mac OS App Store.
• APK – installation package of Android app. Be very careful when you install these on your Android device. Some of them may contain an app with malicious behavior.
• XLSX, DOCX, PDF – Document files can have scripts embedded in them and some of these scripts can have a behavior similar to a virus.
• MSI, DMG - Installation packages for Windows and Mac OS. If downloaded from untrusted website could contain malicious software which will infect computer upon installation.