We use Avast Antivirus on our Macintosh and Windows computers and they have a program that offers free antivirus for students and teachers. Just click on the graphic above for more information.
Another provider of free antivirus software for Microsoft Windows is AVG. Click on the following link to download their software: AVG Antivirus
Microsoft also offers free antivirus to users of the Windows operating system. Just click on the following link: Microsoft Security Essentials
For the specific removal of malware, Malwarebytes provides a free scanner that will remove many malware infections: Malwarebytes Anti-Malware