Starting in 2003, the Department of Homeland Security (DHS) set up a vast network of what it calls "local data fusion centers," 77 in total (or maybe 68, the DHS isn't even sure) — in the hopes of producing solid intelligence on potential terrorists, who would presumably operate from within the country (ie 'home-grown terrorists).
So, the DHS is using tax dollars to log the personal information of U.S. citizens in order to create a vast spreadsheat. Complex 'potential terrorist' algorithms would then scan these spreadsheets and red flag anyone who might be a potential threat.
It's easy to see why in September of this year, after a congressional investigation, Sens. Carl Levin (D-Mich.) and Tom Coburn (R-Okla.) issued a report about these fusion centers basically saying that they're a total waste of money (somewhere between $289 million and $1.4 billion).