The free open source ones seem to suffer from hacking attempts, not sure about vbulletin, when i used to use phpbb people always got hacked.
phpbb is so far from being secure and safe to use to be honest with you mate , vBulletin is high quality forum and don't really get hacked a lot , one of the biggest forums with more then 5m users called epvp is with vBulletin 3.8.7 and It never got hacked as far as I know . at least since I joined
just some DDOS attempts , but I guess that Cloudflare should do the job here
