Virex: Differences Between Compressed and Archive Files

Some utilities can compress an executable file but still allow it to remain executable. When you double-click on such a file, code inside its header decompresses the remainder of file, and the file runs immediately.

If a virus is compressed, it might not be detected by the scanner, hence Virex provides the preference to examine compressed files.

Archive files are different. They cannot be executed directly. If you open an archive file, such as a ZIP or TAR file, no executable files run immediately. You may choose to scan the contents of an archive file after you have extracted them.

Virex lets you scan inside compressed and archive files. Virex supports many compression and archive formats.

This information and more can be found at http://virexhelp.com