I am not sure if this board is kept patched but the version number is 3.5.0 while vBulletin have released 3.5.4 (all security updates), the site isn't very safe then.

Actually, it is very safe. While I haven't done the full update to 3.5.4 yet, I have applied all the other security patches that they've issued up to this point... Thanks for your concern.