found the problem, it wasn't google as such.
I'd not deleted a Joomlaboard forum, and as I had no link to it anywhere thought nothing of it. It was a test board, as the client wanted simple, I got them to go with SMF in the end.
Anyway there where 600 posts about all kinds of iffy stuff, as there was no restriction for membership.
So google was hitting lots and lots of links, they have now been deleted along with the extension, so I'll see how it goes.