If you have a phpBB forum you have probably suffered from robot accounts or if you have it set up Spam guest posts, Now good news i have been testing a Hack for the last 8 weeks, The Anti Bot Question Hack since installing this hack i have totally stopped these little vermin. not one has got though. here is a little info on the hack.
This hack is a variable configurable CAPTCHA to prevent spam bot registrations and spam bot guest postings. A question, randomly selected from a question pool, is added to the registration form and/or the post form for guests. This could be a image, math, general Question or any question you decide. This question must be answered correctly to complete the registration or post successfully. You can create your own individual questions or you can use automatically created questions. The hack is completely administrable via the ACP.
This hack is compatible with Select Default Language. Different questions can be defined for each language.
What this mean to you is no more have to spend time deleting these account or posts from your Board, leaving you free to do something more interesting like doing that bit of Diy you've been meaning to do for months.
you can see it at work at The Showcaserefresh the registertion page to see the question change.
You can get the Anti Bot Question Hack from HERE