Microsoft could have quite legitimately just yanked the app until they could rewrite it without the GPL code. The contractor would be toast (probably had an ind

Microsoft could have quite legitimately just yanked the app until they could rewrite it without the GPL code. The contractor would be toast (probably had an indemnification clause), MS wouldn't have been on the hook for that much even if the copyright holders of the GPL code sued for infringement, as it wasn't willful. The GPL absolutely does not force them to do so. It cannot, as it is simply a copyright license. The GPL actually terminated as soon as MS distributed the code, since they weren't following it's rules. I don't know if they have a formal agreement with the copyright owner, or if they're just following what is an accepted practice in opening the source, but technically GPL v2 cannot be "reactivated" on its own.