Also search for anti-virus reviews. They won't always agree but you might see some common trends. AVG doesn't generally come that high but they include user interface etc as well as its virus-catching abilities. Antivir scores reasonably and I have it on a laptop (which is not actually on-line that much) but it seems OK. Kaspersky (not free) rates highly frequently and I have that on a windows VM on my mac, also so far so good. From personal experience, Norton slowed my PC down considerably but did pick up a number of viruses, online and in emails, but I would steer clear of Norton 360 - it just tries to do too much and you can't disable some of the functions and constant alerts.