I believe our database is backed up at 1AM Eastern. It does lock up the forums for about 30 minutes because of the table type that it is completely locked while backing up. We requested a conversion to a different table type, but the developers said they would not support the change.
We are on a dedicated server.
Looking through the firewall logs, I can see that there have been several DDOS attacks that were eventually blocked on Sunday. Perhaps that was the cause of disruption?
I put a permanent block on the IP range, so they will not be able to access the forums again.