After their initial blustery outrage at yesterday's revelations about PRISM, tech companies, including Facebook and Google, have admitted that they have cooperated with the government, even changing their own computer systems to better monitor users under the Foreign Intelligence Surveillance Act.
The true extent of their participation and the lengths to which they have gone to accommodate the government in surveillance of users is unknown, as employees who have cooperated with the government are barred from discussing FISA requests by law, or even acknowledging its existence. The Times reports that some employees at these large tech companies have even been given national security clearance.
While the levels of secrecy involved makes it hard to paint a very specific picture of exactly what is being monitored and by whom, it's very clear that the tech companies and the government have been working together to create a secret system by which the government can request information on a user and the tech company could give it to them through a secure server (basically the government is being afforded the privacy that users are not). These "lockboxes" are most likely related to the confidential legality of the spying practice, which the Obama administration has asked citizens to trust them exist.
“The U.S. government does not have direct access or a ‘back door’ to the information stored in our data centers,” Google’s chief executive, Larry Page, said on Friday. “We provide user data to governments only in accordance with the law.”
Page is possibly alluding to the "lockbox" creation, which according to a Times source, is the preferred method for retrieving user information, as it doesn't give the government direct access to the company's server.