I recommend AVG Antivirus. You can get a free version which does a fantastic job and you don't have to do much to it, just let it work and update itself!
I have been using AVG the paid version for 8 years now and not a problem! My husband has the free version on his laptop and no problems there either.
Some of these programs require you to set up a lot of things and it can be very confusing, like Norton Internet Security which came with my new HP desktop that I bought last week. It is a 60 day trial and already I am totally confused with their settings! :(
AVG Antivirus ROCKS! Just do a google search and you will find the free version! Good luck! :)