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Dangerous File Extensions

Even though file extensions could be extremely helpful as noticed in the article “What is file extension”, certain dangerous scenarios are enabled by them. With file extensions computer do not need to know what is inside the file – when user double clicks on a file operating system will just open it using a matching application. But in case the file is infected operating system won’t know about it. It will just launch it. That is why it is important to know what file extensions could pose dangers to user computer and how to prevent infections.

Below is a list of most file extensions most commonly associated with computer virus infections:

  • EXE, COM, DLL, SRC – files in portable executable (PE) format may contain a virus embedded inside the file. If a code from an infected portable executable file is executed virus will activate and infect user computer.
  • BAT, VBS, CMD – script files could contain lines to copy a virus and launch it. Certain script files could contain an entire virus code inside.
  • DOC, DOCX, XLS, XLSX, PPT, PPTX – Microsoft Office files may have macros embedded in them. It is important not to allow macro execution without prior knowledge what the macro is going to do.
  • INF – driver and software update information files for Windows. May contain instructions to download infected files to a user computer.
  • MSI, DMG – installation packages for Windows and Mac OS. If downloaded from internet may contain an infected application inside.
  • APK – Android application installation package. Could contain an infected app inside or an app gathering private information.
  • APP – executable file for Mac OS. If downloaded outside of Mac OS store may contain infected code.

The best way to avoid infections is to have an up-to-date antivirus installed on the computer. Also it is a good practice not to install any applications downloaded from the internet websites which you do not trust.