Avast deep scan tries to decend into files that are not archives, thinking they are archives, but often getting far enough to think it's found something and rips it out - destroying the file in the process.
I have lots of disk images of non-Windows systems, a lot of them in ZIP archives as backups - Avast is going through these backups, modifying the ZIPs, and attempting to interpret the disk images with them as archives. I lost the backup of my DOS development system as it found the disk image, and ripped it out of the archive, leaving my DOS system backup dead. Luckily this was after I'd done a bulk backup to offline storage, so was able to copy it back. But, without doing a fill disk search by timestamp and find everything "touched" yesterday I don't know what else has been smashed.
If Avast finds a file, tries to look inside it as though it was a ZIP, and it isn't a ZIP, IT MUST LEAVE WELL ALONE!!!!
Typical list of messages is:
...DiskImages\ABASIC.ssd|BASIC corrupted archive
...DiskImages\armdisk3.adf|Hugo corrupted archive
...DiskImages\6809\FlexBoot.ssd|bboot corrupted archive
...A5000\DOSDEV.zip|DOSDEV corrupted archive
...Backup\MDFS\201807\A5000.zip|DOSDEV.zip corrupted archive
all from it trying to descend into disk images, doing something..... leaving the datestamp changed (which screws up my incremental backups - I've just tried to do a 'recent changed' copy to another machine, and it wanted to copy a quarter of my entire drive), sometimes not changing the contents, sometimes ripping stuff out, some of which I can recover from the virus vault.
