Yep. I'm very familiar with them. Every major anti-spam discussion group has lots of discussions about how they send spam themselves. Look here to see one of them.jechilt said:
Be prepared for it to break (among other things):This looks super cool. Had to use it today and think it is a great idea.
There are lots of other challenge/response mechanisms out there; there's even a patent dispute going on right now as to who invented it and should be allowed to get royalties for it.Any other options out there that are similar?