Top US spook General Keith Alexander, the head of the NSA, told Congress that spying on the internet connections of ordinary people managed to disrupt 50 terror attacks since September 11.
Alexander is a clever man, by touting a number like 50 it sounds rather a lot. It implies that if he was not spying on you, that is 50 airplanes which would have flown into buildings.
He must have been hoping that the members of congress he was explaining PRISM too, did not "do the math".
The September 11 attacks happened nearly 12 years ago, which means that PRISM on average thwarts only a few "terror attacks" a year.
Alexander used the word "disrupt" not "stop" too. This means that the attackers plans just had to be changed because they realised they had been compromised. The number "50" at least seems to be true.
According to "Terrorism Since 9/11: The American Cases," a book edited by John Mueller, a political scientist at Ohio State University, since the World Trade Centre attacks there have been 52 alleged Islamic plots to stage attacks on American soil or on planes bound for the United States. This did not include the Boston bombing.
Mueller said that most of these plots only got to the stage of talking before the authorities broke them up. He added that much of the talking was done with FBI agents. When the US does have a terror attack, it is mostly a shooting.
The big ones have been an Egyptian national who killed two people at the El Al ticket counter. At a Little Rock military recruitment centre, in 2009, an American convert to Islam killed a soldier. U.S. Army major Nidal Malik Hasan, a military psychiatrist, killed thirteen people. In total, sixteen people were killed in these attacks. Adding the fatalities in Boston, this means that nineteen people have been killed. What is telling about the attacks that did go through, was that they were pretty random events committed by loners which would not have been spotted by PRISM technology.
To people over the pond, and indeed in the US, that sounds like a large number of people dead and justification for Alexanders' case for PRISM. In fact it has to be put in perspective with the rest of US crime.
In 2010, to take a year at random, there were 11,078 firearm homicides in the United States, there were 544 homicides by suffocation and 89 by fire, plus 79 intentional poisonings and 52 intentional drownings. Statistically you are more likely to die from malaria in the US than from terrorism.
So when Alexander quoted these figures it should have been seen as a confession. PRISM does not work, and the cost in terms of money, and loss of person freedom. It was created by an over-reaction to a practically non-existent problem which has not actually worked.
What is more alarming is that US officials and lawmakers spent hours publicly justifying the phone and internet monitoring programs as vital security tools and slamming NSA contractor Edward Snowden decision to leak documents about them to media outlets.
Alexander, the head of the NSA, said Snowden's leaks had inflicted "irreversible and significant" damage to national security.
"I believe it will hurt us and our allies," Alexander told the House Intelligence Panel (HIP), which helps oversee the vast surveillance efforts.
While it would be nice if this were true, it is incredibly unlikely. The Congress appears united behind the spying programme and President Barack Obama defended them.
There has been no move to roll them back.
US Representative Mike Rogers, the Republican chairman of HIP did the classic "people do not really understand what is going on" excuse when he chatted to reporters about it.
Alexander said that he would much rather be debating PRISM than explaining how he failed to prevent another 9/11. That would be fair enough if the echoes of the Boston Bombing were not echoing in people's ears.
One cannot help but wonder if all this is worth it. If US people's fear of terror is out of control, it is ruining a country which was once proud of its freedom.
To an outsider, it appears that the overreaction has done more damage to the US way of life than any dirty bomb.