"Websense Security Labs has discovered that Windows Live Mail accounts have been targeted in recent spammer tactics. In these recent attacks, spammers have managed to create bots that are capable of signing up and creating random Live Mail accounts that could be used for a wide range of subsequent attacks.
Windows Live Mail is a part of the Microsoft Windows Live portfolio of services. It is a free webmail service by Microsoft. It was first announced on November 1, 2005 as an update to the Microsoft MSN Hotmail service. Its worldwide release was on May 7, 2007, and roll-out to all existing users was completed in October 2007.
Websense believes that there are three main advantages to this approach for the spammers. First, the Microsoft domain is unlikely to be blacklisted. Second, they are free to sign up. And third, it may be hard to keep track of them as there are millions of users worldwide using the service.
" – Content courtesy of Websense® – Blog: Streamlined anti-CAPTCHA operations by spammers on Microsoft Windows Live Mail