Good guess. Strangely enough, it was spam that got past the spam trap, and looked sort of like it had been posted by hand through a browser. It had even executed the Javascript that sets a deletion password. Plus, it didn't come from proxies, but all from one IP.

Either someone is posting spam by hand, or somebody made a very good spam bot, except they don't bother with proxies for some reason. It's a bit worrying.