WASHINGTON -- The director of the National Security Agency testified Tuesday that the government’s massive surveillance program helped thwart more than 50 terrorist “events” worldwide since Sept. 11, 2001, including a planned bombing of the New York Stock Exchange that involved a Kansas City man.

Army Gen. Keith Alexander, the NSA’s director, made the revelation during a rare open session of the House of Representatives’ Permanent Select Committee on Intelligence, called by panel members to defend and explain government cyber-snooping they support and which they contend has been misunderstood since it was revealed by former NSA contractor Edward Snowden.

Alexander, along with representatives of the FBI, the Office of National Intelligence and the Justice Department, tried to quell public angst over the size and scope of the government’s telephone and Internet surveillance activities following reports in Britain’s Guardian newspaper and The Washington Post based on Snowden’s leaks.

“This is not a program that’s off the books, that’s been hidden away,” Deputy Attorney General James Cole told lawmakers. “It’s been overseen by three branches of our government, the legislature, the judiciary and the executive branch.”

Alexander told the committee that the programs were instrumental in preventing about 50 terrorist “events” in more than 20 countries. At least “10 of these events included homeland-based threats,” he added.

The NSA director said he would provide House and Senate lawmakers detailed information on the 50 events in a classified setting. However, Sean Joyce, deputy director of the FBI, divulged some recently declassified information about two foiled domestic plots.

Without going into great detail, Joyce said authorities were able to crush a plot to bomb the New York Stock Exchange before it fully hatched because federal authorities, through the surveillance programs, were monitoring “an extremist in Yemen” who was “talking with an individual located in the United States in Kansas City, Missouri.”

The individual was later identified as Khalid Ouazzani. McClatchy’s Kansas City Star reported in June that Ouazzani, a local businessman, was part of a small terror cell with two New York men. In May 2010 he pleaded guilty to providing material support to a terrorist organization. He admitted sending more than $23,000 to al Qaida and performing “other tasks” for the group, The Star reported.

Starting in 2007, Ouazzani gave money to al Qaida through Sabirhan Hasanoff of Brooklyn. Another man, Wesam El-Hanafi, accepted Ouazzani’s oath of allegiance to al Qaida, according to federal court records that identified Ouazzani only as “CC-1,” according to The Star.

Court records showed that the three men met in Brooklyn in May 2008 to discuss al Qaida membership. According to the court records, Hasanoff advised Ouazzani not to let his U.S. passport become filled with immigration stamps in order to retain its value to al Qaida. Ouazzani also contacted a consulate in New York after speaking with the other men, The Star reported.

In announcing charges against Hasanoff and El-Hanafi in April 2010, federal prosecutors said the pair had conspired to modernize al Qaida by updating its computer systems, which included buying a software program that helped “communicate securely with others over the Internet,” The Star reported.