President Bush authorised, without the use of warrants, the spying on US citizens three years ago, with the phone calls and emails of possibly thousands of people being secretly monitored since 2002.
Some say that it has helped to prevent specific terrorist attacks, citing the capture in 2003 of an Ohio trucker who planned to blow up the Brooklyn Bridge. Supporters say that radical tactics such as this are needed to combat such a cunning enemy.
Others question the legality of the whole issue, with some NSA officials refusing to be a part of it. The policy was suspended at one point and new restrictions added but soe still maintain that it is a violation of civil liberties and federal law. Source