This is a critical piece of software that must be installed.  On top of that you need to make sure your antivirus software is always up to date with the latest virus definition.  Why the criticallness?  Basically, an undetected virus on your computer, can destroy files, family pictures, music files, business documents, and programs on your computer. In fact, depending on how badly the computer is infected, more than likely the best way to clean out the infection is to wipe out the hard drive and reload the computer from scratc

What anti virus do I recommend?  I always recommend to my clients McAfee or Norton.  To me, both has been around the longest, and they detect and remove virus and certain other threats well.  The other product I have been hearing about and is "better" than McAfee or Norton is  Kaspersky.  I personally have not compared it to the others so at this point I cannot say it is better or not.