Forgot to mention that CIS, CSC and CCE all failed to find anything. Naturally i did a CHKDSK as well and ran CCleaner.
The identical problem appeared on both a 64 bit W7 home computer and an old XP at the office. Both are covered and regyularly scanned by the above Comodo products. Both computers are linked p2p to (different) computers at each location. The other computers in each place do not have Comodo-ware installed by rely on Microsoft's MSE - and the virus does not appear to have been transferred.