Never trusted the fact that reviews on glassdoor AREN'T anonymous...
Oh sure, they hide your name and email, but they have it. A good secret isn't a secret if someone knows it.
I always wondered if they should - and now I wonder if they could - have really anonymous reviews. Just don't tie a review to a user. Sure, ask users to create accounts, validate them, but once they submit a review, it's store without details.
This would make it impossible to respond to subpoenas such as this. And my question now is, could they?