Anti virus/malware programs are usually a must for most PC users so here’s a list of trusted programs for you to use!
1.Spybot Search And Destroy : http://www.safer-networking.org/en/index.html
2.ESET NOD32 Antivirus 4 Gamer Edition : http://www.eset.de/gamer-edition/
3.Norton Antivirus : http://www.symantec.com/index.jsp
4.Avast! : http://www.avast.com/en-au/index
I recommend that you use Spybot if you dont want to use a heavy program but if you wanna be double protected against the naughty stuff you should use ESET + Spybot. Nortons Antivirus use to be pretty awful with its demand on CPU and its crappy detection not working on some viruses not to mention its insane ability to get stuck in your system.