I had used AVAST on the desk top but I also have Advanced System Care and they fought with a lock up happening more often then I cared for - and it's a known problem. I currently have AVIRA as a stop gap until I'm satisfied that AVAST has been fixed - which the developers claim it has. AVAST does work fine on the laptop but that is running XP Pro+ (whatever that is vs the XP that I have on the desk top). I used Norton for years here and at work years ago, but it's too system invasive for my use. McAfee was as bad. Now, it's usually free stuff tho I did upgrade for the $ Advanced System Care after my sweet, charming, lovable, but 'puter illiterate GC 'introduced' some nasty virus's last Christmas.