how is 4ch spam protected?

short question: how do you protect your board from automated bot spamming? i cant see any captcha! normally, from my expirience, a board  would  be instantly spammed to death without captcha or such protective measures. but 4ch board seems to be free of those problems... how do you do that ?

>>25
I had forgotten about the proxy detection system Wakaba has. It's supposed to be rather air-tight. Had any complaints?

I guess with automated backup that'd be workable, although there's still certain (more involved) workarounds.