I bought a copy of the McAfee security Suite and it gave me no end of grief.
I uninstalled it, and downloaded a free copy of AVG.It also scans emails.
Whilst I had no problems with AVG, I now use, SpyBlaster and Ad-Aware. Have been problem free for several months.
On this site you will find that McAfee and Norton seem to cause quite a few problems being embedded in your PC. I am sure that others will swear by it!