Screaming Penguin - Source Does Matter

Whether willingly and knowingly or not, Microsoft is becoming the king of spam.

Several factors contribute.
Hotmail is abused more often than any other mass free email system (this according to my own experiences running mail servers on the Internet) and they dont respond to abuse reports at all. Yahoo, Altavista, and others are also abused, although not as much, and these others respond to abuse reports (Yahoo is very good about it, forward all your yahoo generated spam to abuse@yahoo.com with full headers, they actually look into it.) Combine that with the recent Windows 2000 SMTP vulnerability whereby any user can gain priveleges to control the mail server (and therfore relay spam) and you have a spam junkies dream. They can use hotmail accounts and or relay through any 2000 server. Thanks Microsoft!

For more info on what you can do to combat spam (besides not using Microsoft products) check out http://spam.abuse.net/spam/   Windows 2000 SMTP Vulnerability: InternetNews