reCAPTCHA not keeping out spam bots

at http://forums.epsilonforce.net i have setup a reCAPTCHA as a spam counter measure. Problem is it's not keeping out the spam bots. we get anywhere from 10 to 100 SPAM registrations a day, which rely on reCAPTCHA to prevent SPAM registrations. Even went so far as to change the subdomain of the forum, and it worked to keep them out for about a week. -- You received this message because you are subscribed to the Google Groups "reCAPTCHA" group. To unsubscribe from this group and stop receiving emails from it, send an email to recaptcha+unsubscribe@googlegroups.com. To post to this group, send email to recaptcha@googlegroups.com. Visit this group at http://groups.google.com/group/recaptcha. For more options, visit https://groups.google.com/groups/opt_out.