US defends surveillance tactics in war on terrorism
Officials testify how recently-revealed government programmes led to disruption of more than 50 attack plots, with at least 10 linked to the US

In November 2008, Abid Naseer, a Pakistani student living in Manchester, England, began to e-mail a Yahoo account ultimately traced to his home country.
The young man's e-mails appeared to be about four women - Nadia, Huma, Gulnaz and Fozia - and which one would make a "faithful and loving wife".
Investigating terrorism is not an exact science. It's like a mosaic
British investigators later determined that the four names were code for types of explosives.
And they ascertained that a final April 2009 e-mail announcing a "marriage to Nadia" between the 15th and the 20th was a signal that a terrorist attack was imminent, according to British court documents.
It is unclear exactly how British intelligence linked the Pakistani e-mail address to a senior al-Qaeda operative who communicated in a kind of code to his distant allies.
But the intelligence helped stop the plot in England, and the address made its way to the US National Security Agency (NSA).