A 600mhz laptop that was running really well slowed down so badly, it would not even uninstall the software and had to be reformatted to fix the issues.

Tested on win XP (LAPTOP)dual core Intel 1 gig ram for about a year no issues worked great just lacks password protect!, "but getting better by the day" going to be a great anti virus in full release something to check on from time to time

11-27-08: Installed and ran on Windows XP with Service Pack 3. Was on a system with a 1.3ghz AMD processor and 512mb ram. It installed and ran fine. Would have liked to have kept it for longer to see if it really works as great as it sounds, even though it does appear to be doing what it says it will do. Unfortunately, hence the reason for a 4 out of 5, my computer started to run a little more slowly, and would occassionally freeze - so had to uninstall it(with no problems). If there was more ram in the computer, it probably would have ran with no problem.