Thanks you for the rapid response, which is re-assuring.
I attach the file as requested.
I was finding that Picasa (started using the attached file) was running very slowly. The detection resulted in some difficulties with file 'permissions' and I ended up not only putting the requisite directory in 'exclusions', but finally temporarily disabled Malwarebytes Anti-ransomware (latest Beta).
(I have yet to re-boot that machine with the file excluded and Anti-ransomware re-enabled. The file came from an exact mirror copy on my second PC)
When I did disable MB anti-ransomware Picasa very definitely functioned much more quickly. I wondered if the fact that I was adding photo captions (and so writing into existing files) might be causing some alert????
Any comments or advice most welcome.
PicasaStarter.zip