Antivirus Scanner Software
Where to get it

Updated 4/23/2016

    This is a list of free antimalware scanners that are readily available on your PC, on the Internet, or can be downloaded and installed on your PC.

    None of the software tools in this list are meant to be replacements for your installed active antivirus/antimalware software.
    But if you need an active antivirus program suite see my Internet Security Software Vendors List.

On your Windows PC:

Microsoft Malicious Removal Tool
    If Windows Update is turned on to automatically download and install Windows Updates then a recent copy of the Microsoft Malicious Removal Tool is present on your PC.
    To use the MRT scanner simply enter MRT into the Search box, either in the Start Menu or in the Start Sceen. MRT should be the top or near the top choice.
    IMPORTANT! Run the MRT with Administrator privileges - right-click MRT then chose RUN AS ADMINISTRATOR from the context menu.
    If you have no antivirus scanner software installed this is much better than nothing.

On the Internet

Microsoft Safety Scanner
https://docs.microsoft.com/en-us/windows/security/threat-protection/intelligence/safety-scanner-download

Eset on-line scanner
https://www.eset.com/int/home/online-scanner/

F-Secure Online Scanner for your PC
https://www.f-secure.com/en/home/free-tools/online-scanner

Trend Micro Housecall
https://www.trendmicro.com/en_us/forHome/products/housecall.html

    Simply go to the page(s) and start the scanner(s).
    Note: One or more of these online scanners may require that Oracle Java is installed on your PC or that files be downloaded to your PC.

AntiVirus/Antimalware Scanner Software
(to be downloaded and installed)

Malwarebytes Free
    Available from:
      Malwarebytes site installs Trialware version which will become a free version in 14 days if you do not upgrade to paid version.
      Filehippo Also Trial Version
      Ninite.com
    Note: Ninite will install the free version without trialware. When installing from a download from Malwarebytes site or Filehippo be sure to uncheck the trial version box within the installer or Malwarebyte will eventually ask for payment then quit working if no payment is made.

SuperAntiSpyware Free
    Available from:
      SuperAntiSpyware site
      Filehippo
      Ninite.com
    Note: Be sure to choose the FREE version from the SuperAntiSypware site.

AdwCleaner
    Available from:
      Bleeping Computer site

    Also see Bleeping Computer's Security Utility downloads page for other antivirus/antimalware scanning tools.

Kaspersky's Page of Free Recovery Tools
https://support.kaspersky.com/viruses/utility?CID=acq-freekasp-COM

Finally...
The Windows Club has a fairly comprehensive list of virus scanners.