You still need to worry about infected data on your web server - for the sake of the visiting Wintel browsers!
I had set up the web server on my mac for one project. We had many files meant for Wintel PCs. The first day that the server was up for the folks in the project, someone called to say that his anti-virus program had caught a virus in the data I was serving.
My mac was not affected, but I could infect the unprotected PC visitors. I had to take down the server, download Virex, and clean the data, before I could go online again!
All anti-virus programs rely on pattern matching of the data. So the nice thing is that running Virex on Mac takes
care of other platforms as well.