Comcast gives you free AV, it used to be Mcaffie but now its Norton.

I used to use Norton my whole computer life untill Comcast started this, and I must say back then Norton sucked (resorse hog that didint catch everything :/) but the most recent version is amazing, it will never slow down your computer while you are using it. It waits till you just idle your PC to do any updates/scans and puts them on hold if you get on.