by Sarah Childress

You’ve seen the history of how the Bush administration launched an unprecedented surveillance campaign after 9/11 at the National Security Agency, and how Obama later expanded what had become known as “The Program.”

Now find out how the NSA got all that data.

On May 20, FRONTLINE continues the story of mass surveillance in America in part two of United States of Secrets, an investigation into the secret relationship between Silicon Valley and the National Security Agency.

Companies like Google and Facebook gather massive amounts of data on its users around the world, which they use to sell and create advertisements. To the U.S. government, it is a treasure-trove of information that regularly reveals what we do, who we know and where we go.

The revelations by former NSA contractor Edward Snowden helped to uncover the role the tech industry played — at times unwittingly, but often with consent — in the NSA’s massive dragnet.

So how did the tech giants react when the government asked them to turn over data on millions of ordinary American citizens? And how much do companies like Google, Facebook and Yahoo really know about you?

Find out on May 20 starting at 10 p.m. EST on most PBS stations. (Check local listings.) Watch the trailer above.