http://grisoft.com
I've been using AVG for years now, on my home computers (free version) and on a network I manage (licensed version.) It is superb - but not enough.
You should also be running a software firewall and spyware software.
http://zonelabs.com - poke around until you find the free version of Zone Alarm
There are a lot of good options out there for spyware stuff.
AVG Free is excellent. Norton Anti-virus and Zone Alarm seem to slow computers down a lot. I rely on the hardware firewall built into my DSL modem and so far, so good.
I use AVG, but have had good service in the past with this one:
http://www.avast.com/
Avast!
Look for the "Home Edition."
bump
"Microsoft AntiSpyware offers a capable spyware scan and removal engine that has proven superior to popular freeware offerings like Ad-Aware and Spybot Search and Destroy. Microsoft AntiSpyware goes even further, letting you purge Internet caches, recently used file lists, and cookie files to better ensure your privacy."
Ad-aware, Norton, and this....so far so good.
I've been using Avast for about 3 weeks now. No problems,it works well. Since I'm careful where I surf and what I download, I haven't had any attacks in ages.