comodo
I ditched Norton 360 - too big, slowed my computer down and expensive. Tried Avast, AVG and then Comodo. Got more bang for the buck with Comodo (irony intended). You get anti-virus, internet security and a firewall all free and updates.
Tried to find some malware I knew I had on my son's laptop. Microsoft recommended Malwarebytes, one free trial. Downloaded and it did find two malware programs. On a whim, installed Comodo. It found those two and six more. I think for the price you can't go wrong.
Free Firewall - Download the Best Firewall Protection and Anti-Virus Scan Software from Comodo
Don't know why but the comodo file for XP is larger than for Vista. (at least on the desktop with vista and my son's laptop with XP)
On the down side, once comodo is installed and running, it will aggravate you with pop ups when you download programs or install new programs and/or devices. All good I suppose. Also there are no utilities. Googled free utilities and found the ones that will scan and then charge you for fixes. Went to wally world and found System Mechanic for 19.95 but they were out of stock. Found one in stock at Target - same price. So far it is working well, and you are licensed for three computers.