Do you really think hackers dont know how to get forum files? And, although I dont want to get in a pointless argument, no hackers try to hack small forums softwares because there is no fun in it. They want to hack IPB and vB, the forums out there that are so popular and they can make a name for themselves among the hacking community.
And just to keep promoting PowerBB, it is extremely safe because I do know how to find exploits in PHP and I often report them to the owner and know how to fix them.
Go to PowerBB now!