I'm not surprised at all by this, but Microsoft has been named and shamed as the 5th worst spam service ISP as of the 26th of November 2008 by Spamhaus. They certainly didn't hold back any of their criticism or water down their explanation with pleasantries:

Spam continues to plague the Internet because a small number of large Internet Service Providers sell service knowingly to professional spammers for profit, or do nothing to prevent spammers operating from their networks.

Although all networks claim to be anti-spam, some network executives factor revenue made from hosting known spam gangs into corporate policy decisions to continue to sell services to spam operations. Others simply decide that closing the holes in their end-user broadband systems that allow spammers access would be too costly to their bottom lines.

The majority of the world’s service providers succeed in keeping spammers off their networks and work to maintain a positive anti-spam reputation, but their work is undermined daily by the few networks who, out of corporate greed or mismanagement, choose to be part of the problem.

These are their current rankings for worst spam enabling networks:

  1. cncgroup-hn
  2. hostfresh.com
  3. vsnlinternational.com
  4. gilat.net
  5. microsoft.com
  6. sistemnet.com.tr
  7. cnuninet.com
  8. ecommerce.com
  9. verizon.com
  10. colocentral.com

And their current rankings for worst spam origin countries, again as of 26th November 2008:

  1. United States
  2. hostfresh.com
  3. vsnlinternational.com
  4. gilat.net
  5. microsoft.com
  6. sistemnet.com.tr
  7. cnuninet.com
  8. ecommerce.com
  9. verizon.com
  10. colocentral.com