Everything they do is proven to not be contaminated by "co-mingle", with a signature and paper trail. Plus all core Developers are required to not ever have seen the specs or the code and never to have worked for Microsoft (and any priv'd companies)

Many things they get and do, is protocol watching from Server to clients Samba Server (in various modes)-> Windows Client, Windows[NT|2K|2K3] Server -> Samba Client and of course Windows[NT|2K|2K3] Server -> Samba as Domain Member and such -> Windows Clients

They only do are watching the network traffic using the protocol, as implemented by Microsoft, then as supposedly speced out in the Public Spec, Make changes based on what they see. If M$ tries to claim DMCA or other Reverse Engineering, they are sorely out of luck, they'll open a bigger can of worms than SCO did.

It would be a shame, if Microsoft tried to claim them being contaminated. It would (in the end) force Microsoft to Open up everything in regards to the protocol... to even open source groups.