I was doing the monthly backups of My Documents to an external HDD and suddenly during the copying of one folder an Avast red warning message about a particular .exe file appeared and said it had been sent to the virus chest. The interuption in the copying also seemed to stall the external HDD and as a result it went missing from the desktop.
I restarted the laptop which took an age to shutdown, never a good sign, and when Windows was reloading it crashed almost immediately. A full shutdown and reboot corrected the problem.
The point is that this 'malicious' file has been on my laptop for over two years and, more significantly, has been backed up and copied to both that HDD and various flash drives without incident. There was actually a copy of that same file in another folder on the same HDD from an earlier backup.
I know this file is fine so I added it to the global exclusions list.
I back up everything to two different devices and, you guessed it, when I started copying it to the second device too Avast interfered again. So I added that to the exclusion list.
Here's the cherry on the cake: I decided I didn't need this hassle and as that particular program wasn't required any more I sent it to the recyle bin. What did Avast do? Yup, up came the warning message and for the third time today the .exe file was sent to the virus chest.
This is maddening firstly because of the inexplicable new Avast behaviour to start treating the file as suspicious and not being able, apparently, to tag this particular .exe as OK so that when it is backed up it is not treated as some new threat.
BTW the error message includes an "Add to exclusion list " option. I tried using that to start with but if it did anything there was no indication and apparent change in Avast's treatment of the file.
An option like that requires a confirmation message ie. proof that the action has been enabled. Unfortunately Avast's virus chest also has a similarly unhelpful GUI - when you click to Restore a file there's absolutely no confirmation that has been done. Only if you click it again does it tell you the file already exists.
This is poor GUI design.