PHPbb (http://www.phpbb.com/)
Yes it is unfortunate that their site was hacked but having found out the hard way myself after plugging in every trick I could, their software had too many holes in it and a few silly mistakes that did need fixing. I was particularly annoyed if the database went down that it reported an error complete with the accound user name.
I have so far been very pleased with the simple machines software I am now using with the forum as it not only has more facilities but the security aspect is a long way in front of the old forum I used.
The problem with SM is that the GUI is not as attactive as the phpBB. I had been using phpBB2 Plus version without any problems with hacks, the only thing I encounter is that sometimes; some weird errors are display.
I hope in future that phpBB2 or any other with that GUI, so we can switch back to the attractive one.