You'll want to use a version that is "VM aware" in that it will randomize scan times to distribute the I/O load over time. Otherwise, it could bring your storage system to its knees depending on how many desktops you're running. Trend Micro's OfficeScan was one of the first AV packages to do this. Trend Micro was the very first to integrate with the VSAFE API (or whatever it's called now) to allow real-time scanning in the hypervisor rather than the guest so you only scan data once per host rather than scan it on every single desktop as it arrives. Of course, their Deep Security product is required for that capability, which is a lot more money. Several versions ago it was a jumbled mess of poorly integrated apps that had been acquired from other companies. Very ugly. Having seen a demo of it about a year ago now, it looked like it had matured significantly at that time so it may well be worth the effort to review if you're looking for that kind of functionality.
