I have used Norton, Macafee, Spybot and Microsft Security Essentials. So far Essentials has proven to be the best. Unfortunately any program can only remain current until a hacker figures out how to get around the current program. Once a virus is found the programers can then update to combat the new version of the virus. Some prigramers are slower to react but eventually the software is updated. The worm viruses hide in various files in our computers making it difficult to find. I have found once a worm is found it usually shuts down our virus protection first. Getting the protection back on becomes the tricky bit. Normally I have to start in safe mode or go to a restore point to get the software downloaded again then it's scan after scan in admin mode, safe mode and on every user screen on that particular computer. Last time I was attacked, this method netted 11 Trojan worms all from different scans as described above.
So if we think our protection has picked up and removed a virus think again. If you see the words rogue, win32 or trojan in a scan I can guarantee we dont just have one but many hidden in our files waiting to pounce. Once infected, update your protection program and scan all modes and areas of your computer as you possibly can.