The backup has been restored and everything seems to be working again. This issue ONLY affected forum posts and file and image comments. All other data is up-to-date. Please note that the backup was from 10am GMT, so any posts made between 10am and 2PM GMT today will have, unfortunately, have been lost in the restore process. Apologies for this issue, but if it's any consolation, the table corruption has now been fixed! Yay!
I've been working hard today trying to fix an issue with a key database table that has become corrupted. I still haven't fixed the issue and I'm having to revert to a database backup made about 4 hours ago. This means that forum posts and file and image comments from the past 4 hours will "go missing", never to return.
I've brought the sites back online so you can still use almost all the functionality during this time consuming process, but please be aware that file and image comments will currently be blank. I'm obviously aware of this issue and working hard to fix it!