Follow-up. MSE (on Win7 64 bit) said that it contained a worm:Win32/Boychi.A, but almost all of the 56 engines employed by VirusTotal gave it a clean bill of health, and as I said I have been using an earlier version for 4 years now, so I finally concluded that this was a false positive and told MSE to allow the installation. So far so good. Hope anvir and MS can get their acts together to avoid this false positive (if it is one).