The following file extensions can contain executable code. This means they can potentially carry a virus to infect your computer.

• .ade: Microsoft Access project extension
• .adp: Microsoft Access project
• .bas: Microsoft Visual Basic class module
• .bat: Batch file
• .chm: Compiled HTML Help file
• .cmd: Microsoft Windows NT Command script
• .com: Microsoft MS-DOS program
• .cpl: Control Panel extension
• .crt: Security certificate
• .exe: Program
• .hlp: Help file
• .hta: HTML program
• .inf: Setup Information
• .ins: Internet Naming Service
• .isp: Internet Communication settings
• .js: JScript file
• .jse: Jscript Encoded Script file
• .lnk: Shortcut
• .mdb: Microsoft Access program
• .mde: Microsoft Access MDE database
• .msc: Microsoft Common Console document
• .msi: Microsoft Windows Installer package
• .msp: Microsoft Windows Installer patch
• .mst: Microsoft Visual Test source files
• .pcd: Photo CD image, Microsoft Visual compiled script
• .pif: Shortcut to MS-DOS program
• .reg: Registration entries
• .scr: Screen saver
• .sct: Windows Script Component
• .shs: Shell Scrap object
• .shb: Shell Scrap object
• .url: Internet shortcut
• .vb: VBScript file
• .vbe: VBScript Encoded script file
• .vbs: VBScript file
• .wsc: Windows Script Component
• .wsf: Windows Script file
• .wsh: Windows Script Host Settings file

Add any extension for a document that contains macros, including Microsoft Word, .DOC, Microsoft Excel, .XLS, and Microsoft Powerpoint, .PPT. Beware of .HTM and .HTML files; they may not be safe because they can access the Internet to download unsafe files.

Mac extensions

It's harder to detect executable files on the Mac. Some common file types that may cause problems are Applications (APPL and APPC), Extensions (INIT), Control Panels (cdev), AppleScripts (osas), and files containing macro scripts such as Microsoft Word (WDBN), Excel (XLS8), and Filemaker (FMP5).

The future or viruses

This list of dangerous file types is far from complete, and it changes all the time

It's possible to get a virus that activates just by reading an email. No attachment is necessary. A recent virus known as Wscript.KakWorm spread by taking advantage of a security hole in Microsoft Outlook Express. Many people became infected even though there was no attachment to the email.

I expect to see similar exploits in the future. If you must send email attachments, do it safely. As for me, don't bother to send me attachments of any kind. I never open them.