Ad-Aware Free Antivirus+ is an application that combines anti-spyware with a powerful antivirus.
http://www.lavasoft.com/
http://www.lavasoft.com/products/ad_aware_free.php
https://www.avast.com/
Scroll down the page to find 'Essential - Avast Free Antivirus' and download it.
Anti virus software is a must have for all Internet connected computers.
NOTE: Links will open in a new window or tab.
http://www.avg.com/us-en/homepage
Download AVG Free
Main Website
http://www.avira.com/
Free virus protection for Windows
Avira Free Antivirus
Clam AntiVirus is an open source (GPL) anti-virus toolkit for UNIX, Mac, Linux and Windows.
Information and program downloads for ClamAV
http://www.clamav.net
http://www.clamav.net/download.html#otherversions
ClamWin is free Open Source Antivirus Software based on clamAV for Microsoft Windows.
http://www.clamwin.com/
Download Page
http://www.clamwin.com/content/view/18/46/
Portable ClamWin on a USB or Removable Drive
https://clamwin.com/content/view/118/89/
Free Antivirus that detects and destroys existing and unwanted PC invaders.
Main Website
https://www.comodo.com/
See the Free Products Index to Download
https://antivirus.comodo.com/free-antivirus.php
Spybot - Search & Destroy detects and removes spyware.
http://www.safer-networking.org/
https://www.safer-networking.org/private/details/#Free