Recognizing dangerous file types

This information applies to Windows Internet Explorer 7 and Windows Internet Explorer 8.

Dangerous file types are those that have the potential to contain viruses or spyware that might damage your information or the programs on your computer. The types of files that are considered dangerous are usually program files (.exe), macros, or .com files. The vast majority of files with these extensions do not contain viruses. However, when you download or receive these types of files in e‑mail, you should not open them unless you trust the source or you were expecting the file.

The following are the most common file name extensions used by e‑mail viruses and other malicious software. When you receive files with these extensions, save them to a folder on your computer and scan them immediately with up-to-date antivirus software before opening them.

Most common file name extensions

The following table describes file name extensions that might indicate that a file is dangerous.

Extension Type of file
Extension

.exe

Type of file

Program

Extension

.com

Type of file

MS‑DOS program

Extension

.pif

Type of file

Shortcut to MS‑DOS program

Extension

.bat

Type of file

Batch file

Extension

.scr

Type of file

Screen saver file

Notes

  • Some viruses use files with two extensions to make dangerous files look like safe files. For example, Document.txt.exe or Photos.jpg.exe. The extension farthest to the right is the one that Windows will try to open. It is extremely rare that a legitimate file would have two extensions, so avoid downloading or opening this type of file.

  • There are files that are safer to download than program or macro files, such as text (.txt), or image (.jpg, .gif, .png) files. However, you should still be wary of unknown sources, as some of these files have been known to have specially crafted formats that can exploit vulnerabilities in computer systems.