ESET Hell
I was alerted to this by a couple of users, out of about 60 that utilise ESET.
I didn't make anyone else aware for 2 reasons:
Firstly, I didn't want to make people take a blasé approach to viruses being detected on their computers.
Secondly to gauge the reaction, ie; who will be responsible and say that they're getting warnings of virus detections on their PC's. Only 1 other person contacted me that day...
I found a post on the ESET forum that changing the update mode to allow 'Pre-Release Updates' resolved the issue after a 75MB-ish download.
None of the sites affected utilise the Management Console, so it wasn't limited in that respect.