Norton Antivirus.
But don't buy the SystemWorks, buy the Antivirus program. It is cheaper, and you don't get all the Norton 'programs'.
Seriously, I was a devouted Norton Utilities believer in the old days (DOS, anyone?
, saved my posterior a zillion times. Right now though, unless you go for professional edition and get Ghost, all of the extras are just resource hogs... haven't seen a useful utility in a long time
also, McAfee (network solutions?) ViruScan... those are the two most popular, there are other very good ones but these two get the most talk...
If you're concerned about security in general, download ZoneAlarm from www.zonelabs.com, they have a free version that is amazingly simple to use (install it... done
, and has consistently been rated above such long-time champions as Black-Ice Defender etc... I've had it running in the background for months