[Nat] To play devil's advocate for a moment -- I'm sure the legal dept. would say that's because Microsoft promises protection from such actions, in return for the license fee.
I think that the microsoft license agreement - along with all others in current use, are pretty explicit in saying they don't offer ANY guarentees in this regard. I would love to see where microsoft compensates me for legal trouble that results from using microsoft software.
If I could show precedent where someone attempted to sue users of (or developers who integrated) an Open Source project -- but lost -- that would be a stronger argument.
You probably won't find such a precedent unless someone has actually brought such a suit. If no one has, that would be strong evidence that your legal departments fears are unrealistic. Of course they could say "Well the fact that that no one has sued and lost makes it riskier that we get sued" - LOL. Well, no one has found physical evidence of space aliens - just goes to prove how clever they are. You can never resolve anything with a dumb lawyer. Good Luck Robert Ramey
Such a decision has technical and economic implications far, far beyond what your legal department (and probably management - if its gotten this far) are aware of.
[Nat] No argument from me there.
Maybe more practical advice would be to suggest to your boss that he get a second legal opinion.
[Nat] Interesting suggestion! I'll see if I can make anything happen along those lines.