There are several FREE antivirus programs available. Other forum members can give you more information about them. I use Avira, which has had excellent reviews, but is gradually falling out of favor with me...keeps wanting me to upgrade to the paid version, and doesn't have a decent support forum or a direct way to contact them. Am thinking of changing.
After trying the 30 days  free McAfee antivirus that comes with New Dell Venue 11 pro, is it possible to change and buy a different antivirus?
Change antivirus