My own forum has had the same thing. Most of the Spam is coming from China, so I've had to block the spammers by blocking ranges of the Chinese IP's.
Maybe you can do the same.
Our signup process is just tedious enough that I'm flummoxed it's "worth it" to these people, but maybe in a down economy it is.
In any case, I'm deleting/blocking offending accounts as soon as they pop up. When you see an offending one, just drop me an e-mail with the username, and I'll take it from there.
Contact the Chinese authorities and tell them to please stop so-and-so IP address from spamming with pro-democracy, pro-Tibet stuff.
You'll never hear from THOSE individuals again. ;-)
Seriously, we've had this problem on a board I monitor. It got so bad the owner had to institute the "copy the crazy letters and numbers" thing. It is said the Chinese have created a bot that can autoregister through everything but that - so far.
Most of the Spam is coming from ChinaThis is where things get interesting. We run our own custom anti spam system with my hosting company and, while we see a fair amount of spam from China, a lot more comes from Eastern Europe countries like the Ukraine. We also see tons from spam friendly hosting services like thePlanet/ev1.
There's no one real solution to the problem. Besides a 2x4 of course. :)