A few months ago a McAfee update disabled my internet access. Had to uninstall it and then found it wouldn't reinstall. Long story short, I went to Avast! and Adaware, both in their free versions, and so far so good. You will need to disable the RealTime protection in Adaware as there's a conflict between the two.

I also run Spybot and Malwarebytes but feel the latter is probably redundant.