...with the hopes that the forum databases had been properly updated and nothing would be lost.
We weren't
that irresponsible. We double- and triple-checked beforehand that the forums were backed up and that the backups were intact. We planned to restore the backups the following day and pretend that nothing had happened.
However, GameSpy had screwed up our FTP settings, with the result that we were not able to restore the backups for a month and a half. (Their technical support was unfortunately not very responsive, which was one of the reasons we later switched to independent hosting.) Once we got our FTP account working, everything was back to normal in a few hours. Nothing was lost.
I was the person who actually deleted the forums. A lot of people pointed out to me afterwards that making the forums invisible, inaccessible, and not counting toward posts would have achieved exactly the same effect and not required a forum backup. Unfortunately, that didn't occur to me at the time. Hindsight is 20/20.

well, i searched the forums for something about it and i ended up finding This. What's up with that?
That was when we decided to try something different: putting an0n in the "Voiceless" usergroup instead of outright banning him. Unfortunately, whoever had set up the Voiceless group in the first place hadn't configured it properly. As a result, an0n could view every single forum, even if he couldn't post in them. Fortunately, the only thing he did was post a few screenshots of the admin forum, which were embarrassing but which didn't reveal any sensitive project information.
The security hole in the Voiceless incident was part of the inspiration for the April Fools joke, as nuclear1 supposed.