Cybersecurity

Hello,
I am using a linux fedora 12.0 with L7 filter and proxy as the main firewall for my system composed of some several hundred pcs. The port 80 is open for certain mac addresses these computers, that is to say that , only a few of these computers have access to internet and others have been denied. However, they have access to two specific websites on internet .
I would like to know that if there is a virus attack through these websites in form of executable adwares or malwares, can this linux firewall detect any information that might be directed out of those computers to the attacking source? In other words, is there s tuning in L7 filter or any other filter that can detect transfer of files or some bites through port 80 unrelated to normal http requests?
Thanks

Adding virus scanning to a proxy is a nice idea, but you need a provider of updates daily like Norton and McAfee. If everyone goes through the proxy on a virus protected system, then only the secure connections are an unprotected download problem (because they stream through, generally).

You can block known bad sites, but the list keeps changing. Maybe there is a place you can get the list daily for free.