I used to use NOD32 but it's active scanning technology interfered with my DAW performance. I then used AOL's Active Virus Shield because it used Kaspersky, wasn't intrusive and had almost negligible impact on resources; most importantly, it did not interfere with my audio operations. AOL's move to McAfee spoiled it because, traditionally, McAfee, along with Norton consume a lot of resources. I replaced AOL with AVG, should have been Antivir but I saw AVG now had active anti-Spyware (as a separate app though).