Welcome back to DBF! 
This is not the first time we've had a serious issue with the site and this probably won't be the last time either.  
Due to the nature of computing and the internet there is no way you can ever fully protect yourself against malicious people or software and hardware failures, you can take the best measures possible though and to that end I have learned from past experiences.
As for what happened, it's really quite impossible to guess.. It would be true to say that we were on an older (but not ridiculously old) version of SMF, but it's open source and it's popular which means people are trying to make exploits for it all the time - So it is possible that someone found a way of corrutping our database.  More likely though, is that something else corrupted the database, which is what I think happened, especially if a process was writing to it and it was being restarted.... Though the chances of this type of thing happening are small, these things still can happen.
After the incident with Hostpapa where they deleted our site and my backup had been made in ascii, I made sure we were on a host with automated backups.  Xilo has this service and our site and all it's databases get saved in the early hours of each morning.  Getting us back up and running should have been simply a matter of me rolling back to the last backup, however when I tried to do this I quickly realised that we had missing data... There were corrupt tables which were stopping the database being rolled back.
I repaired the tables and I then raised the issue with Xilo because there were missing posts, they've worked very hard to restore as many of the posts as they can, there may be some missing but there won't be many.  The private messages on the other hand have all been lost and there's nothing I can do to get those back.
I've run a lot of tests over the database, I've also updated the forum software to the latest version & have taken full backups of everything before my update in case I need to roll the site back.
I can't tell you how gut wrenching it was for me to see the site crashed like that... Obviously you all know I've retired myself from coding intros but I regard you all as my friends and this community has been around for over a decade. I want DBF to remain online for as long as people have a use for it and I apologise for the delay in getting it back up!
Anyway, welcome back and hope you carry on enjoying the site 

Shock
Ps: Please also use this thread to report any issues that you find when using the forum and I'll do my best to fix them!