Thank you
r@vast. I have had success in installing Avast Free 22.4 on the Windows 7 system I mentioned earlier in this thread. The logon/logout problem has not yet reappeared. It that situation continues, I will consider that Avast has successfully addressed the problem since Avast 21.
Thank you
DavidR for the insights into emergency updates. I would be surprised if the emergency update facility in version 21.5 was not compatible with an emergency update for version 22.1. I guess that Avast would have this situation covered. I hope so.
With my usual bad luck, as soon as I have posted this the problem will return.
As the man who jumped off the Empire State Building was heard to say as he passed the 70th floor, "So far, so good."