According to spamhaus.org's list of the Top 10 Worst Spam Service ISPs, Microsoft is the fifth most spam-friendly ISP.
The Washington Post reports that earlier this month Microsoft initially debuted at number 9, but with spammers targeting Microsoft's live.com and livefilestore.com properties to redirect visitors the company is quickly sliding down the list.
Spamhaus CIO Richard Cox says spammers flock to Microsoft properties because "they know anti-spam groups are unlikely to block Microsoft properties outright." Cox goes on to say that Microsoft is aware that its live.com system has been supporting an illegal drug sales operation, but has yet to do anything about it.
For its part, Microsoft says:
Using Windows Live services for spam is explicitly prohibited by the terms of service, and Windows Live accounts that are found to be used by spammers are aggressively removed.