Spybot - Search & Destroy
Full user review
"Excellent - none better"
Prevents malware from getting in your computer and finds any PUPs that are in the computer before it was installed. It keeps computers safe from all that crap out there. Best of all - it is absolutely free.
If I ever find any, I will let you know.
I had to get rid of a highly touted paid program I had because it missed 17 PUPs in my computer that it had allowed to get in there in the first place. Some were malware. Spybot S&D found and destroyed all. Best program out there by far.