Whatever antivirus you get, please make sure that it checks all hidden files.  AVG will do this if you set it to. I downloaded a power point with macros on this site and it caused a lot of my files (1,000s) to become hidden.  Microsoft has come out with a new fix for this as they recognized that their office products are vulnerable.  I would get AVG and make sure you look very carefully at the advanced options and set it for all files.  With the virus I got from this site, I lost tons of stuff that I was working on.   Keep in mind that you should only use one antivirus program at a time as they will interfere with each other.  When you install any anti virus program it will make sure that it is the default antivirus program on your computer and may even ask you to remove or turn off the others.