A Short History Lesson: In July 2006 AOL offered a data-bank, containing the data of 20 million search queries by 680.000 AOL-users, for download on its website. Although the data was removed again shortly after, the data had found its way into the net and since then stayed there. This did not only prove as a PR-disaster (the ‘Data Valdez‘ case) but also triggered an interesting legal dispute (Does v. AOL LLC, Case No. C06-5866 SBA (N.D. Cal.; June 22, 2010).
Although the AOL-users had been assigned random numbers to protect their identity it took reporters of the New York Times less than a month to identify at least one user (only) on the basis of the search queries of this user: