The Wall Street Journal reports that there was a break in into Microsoft's internal network and the intruders were:
...believed to have stolen the blueprints to its most valuable
software, including the latest versions of Windows and Office,
people familiar with the situation said.
[...]
The motive behind the break-in isn't known, but industry experts
speculated it could be the early phase of a "data hostage" case,
in which hackers threaten to publicly disclose a corporation's
intellectual property....
While it's a sure thing that M$ would pay to avoid having the world know how ugly their sourcecode really is, it's more likely some poor user out to kill off Mr. Paperclip, once and for all.