|You say you have Avast installed now, there is a free version of Avast and it is generally good. Just make sure that when you install it you uncheck the trial version of the pay version or it will bug you to pay for it. If you have it installed and did not uncheck the trial, just click on "End Free Trial" which will end the trial version BUT leave you with the free version (trying to trick you into not clicking but buying which is about the most annoying they get). Do NOT get a full suite since it rarely has more protection, uses more system resources (really bad on an older machine, but bad on any machine), and often replaces the Windows Firewall with their own (I prefer Windows Firewall). I have used Avast on machines before.|
My preferred antivirus is Webroot Secure Anywhere but you do have to pay for it. If you look carefully at Newegg's specials (I get them by email), they often have specials on Webroot's software download version for 1, 3, or 5 machines for really cheap, sometimes under $15., even for the 5 machines version. I am not connected to any of these products or sellers, I just recommend what I like.
You have to be a little bit crazy to keep you from going insane.