Good choice for a free tool. The pop-up in the corner is slightly annoying but since it's free... And it has caught several nasty's that snuck in, but also has thrown up a few false positives for PUP's, but only in places where files had been downloaded (not system files etc.). Also another suggestion is ClamWin. It is open source and free. It is a little clunky but works great on obscure Win OS'es like 2003 & 2008 server plus all the Windows Clients from XP to Win 8.1. It also runs on Linux as I also have it on 2 different CentOS 6.x boxes.