EPIC Sues DHS Over Covert Surveillance of Facebook and Twitter
epic.org
epic.org
Facebook and Twitter are public outlets, and if you aren't monitoring your privacy on them it's your own fault. If you make friends with random folks on Twitter or Facebook, that person very well might work for DHS - but you didn't have to be friends with them. And if you're running a completely unfiltered account, there's nothing that they couldn't find by using the Twitter Search API anyway.
While the specifics of the program are not declared, they did publicly announce that the program was going on and gave some generalities. Anything further would be basically asking them to reveal either their analysis or their methods...which won't happen and is likely already shielded from FOIA.