The thing about scanning archives is, well, where does it stop? Almost every compression program has its own format. So when do you stop supporting compressed archives? Do you support .tar files? How about gzipped tar files? What if the extension has been changed to .tgz, ala Slackware? How about the two 7zip formats? How about .bz2? These may seem like ridiculously obscure compression formats- but not to your *nix user- and many power users have things like Cygwin or SFU on their windows boxen. Which means those formats will be present, and may need to be scanned. They aren't supported (I assume), because the percentage of users who download them regularly is small. The same with the number of users who download .rar files. Actually, the last time I saw a .rar file was two years ago...