phpbb2 spam question

[joemorris86]

hey guys, im currently using phpbb2 for a warcraft guild site, and every single day we get bombarded with fake sign ups with people offering viagra and stuff like that, its set at the moment so people need to verify their email and they need to type in some characters when registering, but that doesn't help. is the only way to stop this to have admin aproval for all accounts, or is there like an addon with further security sign up measures?

ive banned all the ip's aswell with no luck, still get tons of new signups a day.