After attempting to implement two different 3rd party antispam measures, leaning on IPS's supposedly 'very good' antispam system and generally restricting post counts and interactions on new accounts to a minimum to keep spam down it's still obvious that spam is getting through (and in a particularly obnoxious way).
Admitting defeat, I've enabled the question and answer challenge spam prevention on the sign-up form with two questions currently in the rotation. You've probably seen this a lot on other forums, but in case you aren't familiar the Q&A challenge is simply a single question posed to prospective new joiners that they have to answer correctly in order to sign up. Typically these questions are themed so as to fit that of the forum and confound spammers who probably don't even know what your forum's primary subject is anyway.
I'd like to get this to five questions total and can't really think of anything else that fits the criteria below well so I'm hoping that a few of you can help with suggestions: Please do not post your suggestions here, but instead PM them to me*. I'd rather these answers aren't indexed and easily searchable on our own URL. Free patch (posted) for the 3-4 that're picked.
Remember:
The person signing up might have very little knowledge of airsoft at all
Questions should nevertheless probably be airsoft themed to reduce overlap with these spammer's general knowledge
Answers to these questions should be short as they will be checked against a list of appropriate answers with no human in the loop at all, so if they have to answer with more than one or two words it's probably not going to work
If you want to see the existing questions, here they are:
Not necessarily attached to either question (particularly the second).
*I've enabled post approval simply so that one of you doesn't accidentally spill the beans on a good question.