Can someone explain why Microsoft would go to such length obfuscating the Skype code and taking down derivative work? Is their IP worth the trouble? Do they se

Can someone explain why Microsoft would go to such length obfuscating the Skype code and taking down derivative work? Is their IP worth the trouble? Do they see interoperability as a threat? Are they afraid of misbehaving clients? Surely it's not just a case of a lawyer having too much time on his hands.