The good news is that, according to Canonical, the root cause of the breach has been identified, the forums software is being reinstalled from scratch, and no posts, private messages, and so on will be lost as part of this process.
Another good news is that the aforementioned hacker - although, to be fair, it could also be someone impersonating him - has announced that the forum users can rest easy as he has no intention of publishing them or using them in any malicious way.
He also confirmed that they were encrypted with the default vBulletin hashing algorithm (md5(md5($pass).$salt). "Whilst it may not be the strongest, when you're dealing with 1.8m users it would take a very long time to get anywhere with the hashes," he wrote on Twitlonger.
"You don't have to worry about a DB leak," he added. "That isn't how I like to do things. If I do get into a website, most of the time there's no REAL malicious intentions. Grab the database, leave a message. That's it. I don't like to over-do things. Might cause some downtime, but what if it WAS the 'syr14n c3b3r 4rmy' (not that their brain-dead brains have the power to do anything whatsoever), and they did have malicious intentions, and they did leak the database and use it to their own advantage?”