Anti-Virus
Anti-Virus programs are software programs that prevent files containing viruses from running on a computer, or software that detects, repairs, or removes virus-infected files form a computer or computer network. Two things to remember with anti-virus programs are : update your virus definitions often and scan often.
Probably the most widely used, excellent user support and tutorials. Costs an arm and a leg to buy the program and subscribe to the virus update files.
Another widely used program, not very reliable in my experience, but effective. A fee is involved in using this one also.
The MOAB of anti-virus programs. FREE to use and VERY reliable!!! Click on link and explore web page until you find the free version of AVG.