Microsoft says that some of their computer systems, including some in their Mac Business Unit, were penetrated in the same way that Apple and Facebook were earlier this year.

This would normally only count as a Level Two attack, but it has been upgraded to a Level Three for the coordination involved.

The infection vector, as in the Apple and Facebook attacks, is a forum for mobile developers that had been compromised (unbeknownst to the maintainers) for several months. As in the other cases, Microsoft insists that the impact is limited and no customer data was affected.

• ArsTechnica: Microsoft joins Apple, Facebook, and Twitter; comes out as hack victim
• Reuters: Microsoft says small number of its computers hacked
• Gibson Index:
  • 2013-02-15: Facebook Malware Incident
  • 2013-02-19: Apple Computers Hacked