This problem is showing up in other forum message boards hosted by other services. One forum I am an admin at has been seeing adspammers who are not only able to evade the Captcha device, they also are getting past email verification in setting up a user account.
It is a pain to deal with, and we're not sure what a long term solution is unless the host of the forum servers makes modifications to deal with these latest evasions. Just a FYI.