Every organization of any size since time began had their spies. It was nothing new. Of course there existed some within the ranks of the Resistance. Hermione just wish she knew which ones were suspected. She had a few theories, but without knowing more, she couldn't be sure. Certainly William Wood wasn't looking like a really trustworthy member after teaming up with his old friend to try to murder her. Or perhaps Aberforth was resentful that none of his fellow Resistance members helped to get him out of prison. It could be anyone. Speculating wouldn't get her very far.