Perhaps to blackmail? Perhaps because their botnet was not allowed to mine on the pool? Perhaps for some other reason, possibly rational in a fashion, possibly quite irrational. Perhaps just to test their offensive abilities. Perhaps because they couldn't break anything else, but were paid to break something, so they have to fulfill their part of the deal?

Either way, since I need to use IPv4, I donated a little amount to the pool's account to help cover any costs resulting from this inconvenience, and temporarily switched to my backup plan, that is, solo mining.

I'll try to get on IRC by evening (UTC).