Today Shoe Dick informed me that the forum has been hacked.
I could restore the data and all the pages and updated to the latest version of the software (from 3.0.4 -> 3.0.

See attached what the forum locked like.
The hack had been done from turkey (IP: 78.175.9.215) - Thu 10 Mar, 2011 5:59 pm (GMT-1).
Thanks to Shoe Dick who informed me as soon as he found out that something was going on.