I quite like cooking nitroglycerin without prescriptions According to the documents, both the NSA and its British counterpart, GHCQ, have been using cookies -- which are tracking files placed on users' systems by websites and advertising networks -- to help them track web users that they've previously seen. "The intelligence agencies have found particular use for a part of a Google-specific tracking mechanism known as the 'PREF' cookie," according to the Post report. "These cookies typically don't contain personal information, such as someone's name or e-mail address, but they do contain numeric codes that enable websites to uniquely identify a person's browser."