Otherwise it would just be an SCO tactic. And I very much doubt SCO will be successful, because that would mean anyone can point fingers at anyone with no proof/evidence whatsoever.
That's just the thing. Regardless of the outcome of the lawsuits, SCO has ALREADY been highly successful. They have had the chance to plaster FUD everywhere. They have managed to slow the adoption of Free software, and, somehow, they have even found a few sympathisers along the way.
Now, imagine Microsoft launching a similar campaign. They already have the size and employment numbers. They already have the US government in their pocket. They could probably win the FUD campaign AND the lawsuits against pretty much any target they choose.... Regardless of the facts. Image is everything. Facts can say whatever you want them to.
What if the leaked code actually contained MS code taken from Linux? Let's say some lazy Redmond programmers stole a few routines and took an extra vacation in the time they saved. Well, those segments happened to be in the "leaked" code. Now it's just a "he said / she said" argument over who wrote the code.
Don't get me wrong. I don't think Microsoft will go out and use this technique except as a last resort... But a painful doomsday weapon it could be....