The forum message says:

"The Following PHPBB Forum was disabled for security reasons. If you are the webmaster of this forum please contact support for more detail."

I am 90% sure that forum has been hacked. Several months ago, PHPBB forum software, excellent software was hacked and hundreds (thousands) of forums were wiped out by the virus. This might be that virus if they did not update their forum software to fix the bug. Or a new one.

Reason I saw this is it says "If you are the webmaster of this forum..."

The webmaster would know about it if he took it down for a security reason. In other words, the webmaster is the one who would take it down. That doesn't make sense.

I hope it's not true, else he could have lost his entire forum.