Be careful what antivirus and antimalware software you install because they can conflict. You can only have ONE antivirus installed at a time. If you find you installed conflicting software you will notice that it takes considerably longer to do anything at all. At this point be patient and uninstall some software until you have 1 good one remaining.
There is a Safety Scanner by Microsoft that I came across on their website here that will do a scan on your computer to detect some virii and malware. The program expires after about 10 days due to the virus/malware detection needs updated by about that time. Microsoft does state that this program is safe to use with existing antivirus software.
Visit Microsoft Safety Scanner
FREE Anti-Virus, Anti-SpyWare, Firewalls.
Avast: Free Anti-Virus. More products offered for a cost. Chance for trial versions.
Malwarebytes: Free Anti-Malware. More products offered for a cost. Chance for trial versions.
Zonealarm: Free Firewall. Zonealarm changed their 2015 Antivirus into a paid version. You can still grab their firewall free of charge but everything else will cost. If it is still available you can get a trial version of some of the software to test out before purchasing.
Lavasoft: Free Anti-Virus. They also offer paid versions with many more features.
Microsoft Security Essentials: Free Anti-Virus and Anti-SpyWare. Not used for Windows versions 8 and up.
Windows Defender: Comes with Windows versions 7, 8, 8.1, and 10. For Windows 7, 8, 8.1, Defender is a Anti-Malware program. With Windows 10 Defender has been loaded up with an Anti-Virus as well. Starting with Windows 8, Defender replaces Microsoft Security Essentials.
As with anything, shop around to get the features you want for the price you do not mind paying. Think before you buy as some products offer a big discount if buying multiple copies for your household.
More to come when I get around to comparing and testing.