How come there are so many spam bots registered on here, when I need 20 attempts at the captcha test.
Spambots
Somewhere out there, there is someone with lots of time to spare....
They should be coding in MoSync instead - more intriguing, more profiable & more fun 
Give me an access to forum as an admin. I will fix this issue A.S.A.P
I don't think we'll ever give even moderator access to non-employees.
Still, out of curiosity, how would you fix the spam problem?
1. Make sure you are using the GD CAPTCHA not the older version
* Check your adminCP > Visual confirmation settings >
GD CAPTCHA = Yes
GD CAPTCHA foreground noise = yes/no
GD CAPTCHA background noise x-axis = nnn
GD CAPTCHA background noise y-axis = nnn
Change those to suit - you can see the example/preview below of how it will look. Try not to use the default settings, if they break this system it is the default settings which will get broken.
2) Upgrade your phpBB to v3.0.7 coz 3.0.4 got an issue with spambots
3) Block an access for specific users to post a link with this MOD: http://www.phpbb.com/mods/db/index.php?i=misc&mode=display&contrib_id=9975
OR this MOD to Disallow post links before x number of post(
: http://www.phpbb.com/mods/db/index.php?i=misc&mode=display&contrib_id=10315
4) ATLBL Antispam
http://www.phpbb.com/mods/db/index.php?i=misc&mode=display&contrib_id=14335
Make sure to install all of them to have more secure phpBB forum 
Btw instead of us phpBB, please use punBB 
Thank you for the advice.
GD CAPTCHA is already active. I'll see about upgrading our phpBB as soon as possible.
As for user blocks and blacklists, I don't think they'll do much good.
PunBB looks cute, but it lacks features that we use.
try out http://www.stopforumspam.com , it really helped us to get rid of spammers.
They also have a plugin for phpbb http://www.phpbb.com/community/viewtopic.php?f=70&t=1349145
all the best