I had my username hijacked by a spammer once. It turns out that my ISP at the time had converted from Linux servers to MS after they got bought out, "for security reasons". Apparently they had too much of it ...

Anyway, I immediately changed ISPs (to one running BSD), told them why, and told them I was recommending the same thing to all my friends. My friends scoffed ... until Code Red and Nimda hit the next month.