Our government collects a lot of information about us. Tax records, legal records, license records, records of government services received-- it's all in databases that are increasingly linked and correlated. Still, there's a lot of personal information the government can't collect. Either they're prohibited by law from asking without probable cause and a judicial order, or they simply have no cost-effective way to collect it. But the government has figured out how to get around the laws, and collect personal data that has been historically denied to them: ask corporate America for it.
It's no secret that we're monitored continuously on the Internet. Some of the company names you know, such as Google and Facebook. Others hide in the background as you move about the Internet. There are browser plugins that show you who is tracking you. One Atlantic editor found 105 companies tracking him during one 36-hour period. Add data from your cell phone (who you talk to, your location), your credit cards (what you buy, from whom you buy it), and the dozens of other times you interact with a computer daily, we live in a surveillance state beyond the dreams of Orwell.
It's all corporate data, compiled and correlated, bought and sold. And increasingly, the government is doing the buying. Some of this is collected using National Security Letters (NSLs). These give the government the ability to demand an enormous amount of personal data about people for very speculative reasons, with neither probable cause nor judicial oversight. Data on these secretive orders is obviously scant, but we know that the FBI has issued hundreds of thousands of them in the past decade -- for reasons that go far beyond terrorism.