I do not know what Brion did, but hail to him. He solved it for now. I hope we will find a permanent solution before it happens again. Captcha's for open proxies seem like the way to go for me personally. Otherwise a system of emailnotification for open proxies?
If it is technically feasible you could even make it such a way that the first 10 edits from an open proxy need to b spaced one minute apart. That way a vandalbot would not be able to wreak havoc instantly.
Waerth/Walter