In our experiment, such data was recorded and collected from an extremely large group of users under legal agreements with them. Information which could be used to recognize their identities was not included. By integrating the data from hundreds of millions of web users, we can build a user browsing graph
"under legal agreements with them" ... this makes me nervous. Because I'm one of those people that skim over all the Terms and Conditions and click "I Agree" at the end. Was I unknowingly one of the users in that "extremely large group of users"?
It's not clear whether their "extremely large" group of users is the same as the "hundreds of millions of web users" mentioned in the following sentence. "Hundreds of millions" kind of implies "everyone", like maybe everyone using IE, Hotmail, Windows Live Messenger, etc.