Spam Problem?

[Bacon Butty]

Despite taking a good amount of prevention methods, I have recently had a surge in the amount of spam accounts registering - although, the majority dont post? - possibly due to having disabled the posting of links until 5 posts have been made.

I know they are spammed accounts because literally 9/10 signups as of late have the date of birth as 1st Jan 1980 and bizarre usernames/emails.

Theyare suspect in that they all seem to have a date of birth as 1st Jan 1980 and bizarre usernames.

To signup they have to answer the question 'are you human', where they have to type yes/ye/yeah etc in the box to verify. I also have the Check4SPAM mod installed.

I am at a loss how to prevent such sign ups.

Could anyone please give me any advice?