If that's your own server, please update and patch. Download an
IDS (Intrusion Detection Software) to detect intrusions made. Check
your logs to see if there's any suspicious activities going
on.
If others are hosting the forum for you, contact the host's
admins.
If the host's admins aren't willing to do anything, change to
another host. It's not worth compromising people's data because of
that. Do a backup before moving everything to another host.
