Pejorative term for an internet service provider that permits or even encourages spam mailings from its systems. The plural is spamhausen. There is a web page devoted to tracking spamhausen.
The most notorious of the spamhausen was Sanford Wallace's Cyber Promotions Inc., shut down by a lawsuit on 16 October 1997. The anniversary of the shutdown is celebrated on Usenet as Spam Freedom Day, but lesser imitators of the Spamford still infest various murky corners of the net. Since prosecution of spammers became routine under the junk-fax laws and statues specifically targeting spam, spamhausen have declined in relative importance; today, hit-and-run attacks by spammers using relay rape and throwaway accounts on reputable ISPs seem to account for most of the flow.