I thought captcha was beat last year, and no longer used? Did they fix that/improve it?
The rotation of Q&A are industry related to the purpose of the forum. It's unlikely that a spammer would know any of the correct answers.
I havent had any other mysterious accounts yet, from the above concern, but will be keeping an eye on it. There are remnants of a couple old scripts with some files left behind, which I will purge today - just in case one of those is the culprit.