Thank you. These are on a Macintosh. My PC tower deleted or quarantined the files, rendering them useless. However, I did find a Mac anti-viral program other than Avast, and that did remove the viruses and preserved the file integrity. It's free to download and update and run. SOPHOS.
After using "SOPHOS", which works on 10.4.11 OS and higher, Avast did not detect the viruses.
Yipppppeeeee !
(But I still want to know why Avast Free Edition did not work)