According to Redacted News, the leaked emails showed how names can be cross-referenced across social media sites to collect information on people and then used to gain access to those social ciricles. The emails also talked of how Facebook could be used to spread government messages:
Even the most restrictive and security conscious of persons can be exploited. Through the targeting and information reconnaissance phase, a person's hometown and high school will be revealed. An adversary can create a classmates.com account at the same high school and year and find out people you went to high school with that do not have Facebook accounts, then create the account and send a friend request.
Under the mutual friend decision, which is where most people can be exploited, an adversary can look at a targets friend list if it is exposed and find a targets most socially promiscuous friends, the ones that have over 300-500 friends, friend them to develop mutual friends before sending a friend request to the target. To that end friend's accounts can be compromised and used to post malicious material to a targets wall. When choosing to participate in social media an individual is only as protected as his/her weakest friend.
