Ok, like I've said in other posts most big security companies give you a false sense of security and get you to pay hundreds of dollars a year for there products that do absolutely nothing for your computer. I'm going to show you some very good and free security software that will protect your computer a lot better then MacAfee or Norton.
AVG AntivirusThere is other free anti virus software that does just as good a job as AVG, but AVG has my vote overall mainly for its simle interface and very little memory usage.
Donload HereSpybot S&D/Ad-Aware SEThese two anti spyware programs are free and very effective. I do recomend that you run both programs because one program can cath what the other misses, overall there both very efective/
Download Adaware HereDownload Spybot HereZone Alarm Free EditionPersonally, I don't use a firewall because I have a hardware firewall in my router but this firewall comes highly recomemded from many other users.
Download ZA Here