It's pretty much a public secret that Ballmer was one of the last reasons why Microsoft did not participate much in the OSS community even though a lot of employees wanted it.

To give a concrete example of the changes (heard from a former Microsoft employee): Under Ballmer they were not allowed to touch anything open-source. Pretty soon after he left that was changed to a policy that a BSD/MIT open-source solution must be used if it is available unless there's a damned good reason.