I have Windows XP running in a VM as a screenshot factory for browsershots. Since that involves the machine opening browsers with websites not under my control regularly I recently had it compromised. Not a big deal as I had a clean snapshot, but I installed Avira AntiVir after that. Works fine so far (as fine as AV software can work) but before the program pesters me I thought I'd run a full system scan for good measure.
Performance dropped deep into a bottomless pit, somehow. The system in the VM wouldn't react for a long time and finally (I decided to give it a try and run it overnight) stop doing anyting entirely, the VM display also messes up very funnily. The host system was fine, CPU utilization was also not over the top (apart from the occasional 100% spike VBox seems to have sometimes).
This happens reproducably every time I attempt a full system scan and I've given up by now.
Any idea what could cause this? Are there any better free AV solutions that work well in VMs? I'm a long-time non-user of such software and thus don't have any idea what currently can be recommended and what not.