Huge increase in spammer sign-ups
 

Has anybody else noticed a significant increase in spammer sign-ups in the last few days? We're deleting at least 10 a day on one of our boards. We've got custom human verification via a custom question & answer set up. I changed the question less than a week ago* but it hasn't made any difference; it's as if there are humans behind it that figure out the answer right away and keep on signing up. They always sign up with a different email and IP.

This brand of spammers rarely posts; in 90% of cases they just sign up and you can only tell that they're spammers by their advertising signatures* which they always fill out.

This has been really annoying me lately because the custom question has worked well for us for some time* but now even this is useless. All the captchas have been broken ages ago so we stopped using them as they didn't do anything to lessen the number of spammer signups.