Why, thank you
No, not simultaneously. We had one PC that infected a bunch of USB memory sticks, and we loaded different AV SW on different PCs to see if anyone stopped the virus from entering the PC upon insertion. They didn't.
We have 130ish computers, factory OS, manual setup, XP Pro 80%, Vista Business 5%, Win 7 Pro 15%. All new PCs are set up with Win7 Pro. Windows Update set to run automatically, but are hindered at user's whim (yes, they have admin rights). They are in a workgroup, hence unmanaged. The AD and workspace is accessed via Citrix. Trend AV and FW is up to date, setup in a client server configuration. We're on a slow and steady track to make the PC client environment managed, a year from today, but I guess we have to fast-track that.
The more I read and learn, I understand that given the infection we got, we have to wipe the computers and reinstall. I lean more towards getting advice about detection, safe data backup from infected PC and reasonable countermeasures. I think I can elaborate on that in the appropriate subforum, maybe "Am I infected? What do I do?".