I know that this forum uses Phpbb, like I do, and in the past, I've had problems with spam, as well, so I researched some links that might be useful in fighting it, and I came up with a good one, so I thought that you might want to take a look at it also and see if any of those solutions might help with the spam currently on this forum:
http://www.phpbb.com/community/viewtopic.php?f=18&t=393503&st=0&sk=t&sd=a&sid=b4188c6deeffa81294a38110a98d6761
While I didn't look at the link above... I've personally found that changing the directory in which your phpbb resides makes a MAJOR difference.
Example:
Instead of zalanthas.org/phpBB2
Use a directory name that isn't common, such as:
Board, boards, phpbb php phpbb2 forum forums gdb.
Try something like...
Mantis or something, give the forum a name and use it as the dir name.
These spam bots mostly look for the most common directory names to invade and dig out the php file.
Another thing you can do is something simple, like add a question to register an account that is game related, very simple such as:
How do you spell allanak, or something like that.
Who is the ruler of Tuluk.
Something simple to keep spam bots from knowing that only a player would know.
The spelling one is great though :)