The US monitors all online activity flowing through servers of nine internet firms to track foreigners for national security threats. But authorities insisted the internet surveillance conducted by the National Security Agency (NSA) and the FBI was legal, approved by congress and targeted only foreigners.
President Barack Obama defended phone and internet surveillance citing bipartisan support for it and judicial oversight.
US-based servers of Microsoft (Hotmail), Facebook, Google, Yahoo, AOL, Skype, PalTalk, Apple and YouTube come under the purview of surveillance
programme run under the codename PRISM, according to The Washington Post.
The Guardian had earlier reported the NSA has access to all phone records of service provider Verizon. Later, it turned out, it has records of other service providers too: AT&T and Sprint.
James Clapper, director of national intelligence, whose office oversees the NSA and all other intelligence agencies, said: "Information collected under this program is among the most important and valuable foreign intelligence information we collect, and is used to protect our nation from a wide variety of threats."
PRISM was born seven years ago as an improvement upon warrantless domestic monitoring.
With new safeguards like clearance by special courts, and congressional review, the program accounted for 1,477 items in President's Daily Brief in 2012. Nearly 1 of every 7 intelligence report from the NSA is based on material drawn under PRISM.
According to congressman Mike Rogers, a Republican who heads the House intelligence committee, the surveillance of phone records prevented at least one act of terror.