A while back, the Washington Post reported on a set of leaked NSA slides that most people seem to have ignored.
There was one interesting piece of data in the report that I think deserves more attention. On the slide titled “Address Books” is a table setting out how many people’s address books have been collected, and how many are “Attributed” — that is, how many allow the NSA to tie an online ID to a real named person.
Here’s the data as a table, to make it easier to read:
Notice that Facebook is far and away the NSA’s best source of information about you and your friends. Doing the math, 79437/95086 = 84% of the NSA’s information linking named individuals to their friends online is sourced from Facebook.