[GekkePrutser]

It's good too that they tend to change because they'll soon get blocked for signups.

Like bugmenot accounts that only last a day or so.

[zozbot234]

Services tend to be blocked when they get abused by spammers. So if you want something like this to last, it would make sense to heavily leverage either plain old CAPTCHA's or the newer privacy-preserving "proofs of human presence".