Originally posted here by groovicus
Since I am admittedly a moron, could you elaborate on this further?
Greetings:

Performance, plain and simple. A webserver that's got AntiVirus Software installed locally is going to cause a serious performance hit, especially on sites that allow file uploads (which is the main reason why you'd want AntiVirus for the webserver to begin with). You can also run into problems when a client is connecting to the webserver and trying to access a file that the AntiVirus software is trying to access at the same time.

Also, many websites store uploaded data in a database, and not as part of the file system. This can cause AntiVirus Software to never detect them at all. While you might not be infected, files uploaded and stored in your database may be, and you'll then pass them along to your users who are downloading those files. People will just LOVE you then

A MUCH better solution (and the only real solution in my eyes) when you're dealing with protecting servers from viruses, is to install a NETWORK AntiVirus solution that can monitor everything using its own dedicated resources.

Since your servers are firewalled appropriately (which they should be), and no one is surfing around websites or checking e-mail locally on the servers (which they should not be), the only real way you have to worry about viruses getting on the server is by users uploading them via features on your website that allow such things. And, this is EXACTLY where installing the AntiVirus Software locally will cause you problems.

There are products out there that claim to be made for webservers, but the ones I've evaluated are "clunky" to say the least, and they ALL cause performance hits for the server. Also, they all have the problem of not really being able to detect infected files stored in a database.

Network AntiVirus Software is your friend