Thanks. I'm already trapping and blocking them well.
What I'm wondering is how can they be effectively stopped from trying at all, especially from ISPs, as when I do a block, even if temporarily, it can trigger false positives with real human users.
Ideally, I would like for the ISP to quickly see the problem and stop it on their end, so I won't ever have to consider blocking them. What I want is for Comcast especially to wake up and start taking these spambots seriously.