The following applications do an excellent job of cleaning up extraneous files, spyware, and viruses in Windows. These freeware versions do not
usually scan at user-defined times (the paid versions do). It is better to run them one at a time, preferably in the SAFE MODE, but I have not (yet)
encountered problems with running them concurrently overnight as an administrator and in the regular mode.  Before running them open them with
administrator priveleges and click on Update icons  (paid versions usually update automatically). Because automatic updates can interrupt what
you are doing I  recommend  that you deselect automatic updating where possible. Purifying an entire computer will typically take several hours
and I therefore run them simulataneously overnight . DO NOT INSTALL MORE THAN ONE ANTI-VIRUS PROGRAM - otherwise they will interfere
with one another and, at best, slow down detections.

Deletes detritus left over by sloppy or nefarious programming. I liked it so much I bought the paid version (ca $55 for 3 computers),
BUT THIS APPEARS TO BE A SCAM - when installing the purchased version the supplied registration number is never
asked for. Apparently you pay $55 and get the same product as the free version, with continued messages asking you
to "upgrade" to the paid "pro" version.

Excellent. Thorough and (remarkably) unobtrusive. But Zone Alarm  is better.

AVAST ANTI-VIRUS   (Recommended)
Recommended by Consumer Reports.

A superb firewall plus anti-virus package.

Cleans out unnecesary files, browser cookies, etc. Also the only reliable resgistry cleaner I have encountered. You should repeat executions
until nothing changes (MS Internet Explorer files are especially stubborn).

Removes malware that it claims many others do not.

Allows immunization against known spyware - a big positive. CAVEAT: the subroutine Teatimer does a check at each login
and thereby slows boot up time a lot. If you keep to a regimen of SpyBotting once a week or so you can remove Teatimer and reduce
boot up time. To remove Teatimer: (i) Click on Mode and select Advanced; (ii) Click on Tools and select Resident; (iii) Uncheck Resident
Teatimer. When updating be sure to uncheck any teatimer download icon.

Excellent but you will get nagged about upgrading to the paid version.

Stops Malware running to allow its removal. Can be run less frequently than those above.

Removes specific rootkits. Can be run less frequently than those above.

SECURITY TANGO (Windows, Linux, Mac)
An orchestrated sequence of tasks to rid your PC of the most persistent malware. Print out the list of instructions
before using. This site also contains links to much freeware. However, the red-underlined links above to security apps
will  remove almost all malware.