Further googlings yield these two comments, from separate people in blogs. But be warned, I'm only quoting them and can't guarantee accuracy:

- Clear the IE temp files, from IE's Tools->Internet Options->General->Temporary Internet Files, and it's gone.

- This is not a virus and not a Trojan. It is an IFrame Exploet code in the HTML and it was
blocked from writing and thus doesn't exist on your PC.

Off to PM JiK now...