Personally I support PHPbb, some people can say what they want, but there are more mods/hacks for phpbb than VB. They are all free unless you want something custom designed.
Endless support, some people comment that phpbb, can not be successfully managed as you get to a indepth amount of posts, but phpbb has over 1 million 500,000 posts and over a million replies on it.
(you do have to know some simple php coding in order to mod it the way you like that is only down fall)
It does get hacked it seems more than other forums, but mostly due to people not updating the software when the updates come out, I personally have never had one hacked.
Good Luck with your new forum.