My nephew is a techie with his own business. On my husbands computer his Norton was expiring soon. Was going to be $73.00 to renew. My nephew told me not to renew but to use
http://wwwmicrosoft.com/security_essentials/ it's free and he has used it forever and has never paid for an antivirus ever. I installed it in my DH computer and after running the scan it came up with 4 trojans that Norton's didn't find. When my computer expires from McAfee, I will uninstall McAffee and install the Microsoft security essentials.
He also had me download
http://www.malwarebytes.org/ the free program. This one takes out a lot of adware/malware. You have to run it yourself, so once a week I do that. My computer works great. And it's several years old.