nsa computer desk
© Rick Wilking / Reuters
Booz Allen Hamilton has hired an ex-FBI director to launch an external review of security and staffing procedures after an employee stole up to 500 million pages of data, marking the second NSA breach in just three years since the Snowden case.

Craig Veith, Booz Allen vice president for external relations, said on Thursday that Robert Mueller, who became director of the FBI one week before the 9/11 attacks and led the agency for 12 years, will conduct "a fair, objective and thorough review," according to the Wall Street Journal.

The announcement came after Harold Martin III, a former Booz Allen employee and US Navy veteran, was charged in what is believed to be one of the largest classified data breaches in US history.

Edward Snowden's case is likely to pale in comparison to that of Martin's when it comes to the number of documents stolen. Prosecutors said that Martin had taken as many as 500 million pages of top secret information, which equals 50 terabytes of data, along with six more boxes of files, many of which were reportedly left open in his house or car.

The man, already dubbed 'the second Snowden', had nothing to do with blowing the whistle on NSA surveillance activities, his lawyers argued. Instead, they described Martin as a "voracious reader committed to being excellent at his work," according to the Washington Post.

Martin's attorney, James Wyda, told a US magistrate judge last week that gathering terabytes of classified information "began as an effort to be better at his job," adding that he is "a compulsive hoarder" rather than a "traitor."

Prosecutors insisted, however, that Martin remain in custody, alleging they found the names of US intelligence operatives in the files stolen by the former Booz Allen employee, citing a particular threat to the safety of officers working undercover abroad.

Commenting on Mueller's appointment, Booz Allen vice president Veith said that "we are an organization that prides itself on constant learning. If there are areas where Booz Allen can improve, we will address them."

After leaving the FBI in 2013, Mueller became a visiting professor at Stanford University where he focused on cyber-security issues.

Questions, however, still remain about how these breaches could happen twice in just three years despite the company's assurances of learning lessons and improving internal control after Snowden's revelations that shed light on NSA wiretapping activities in the US and other countries.

Coleen Rowley, a former FBI agent, told RT earlier in October that the number of US citizens having top secret clearances or access to classified information "has soared" through the years.

"The last I heard it is something like five million Americans have been cleared for classified information. So, any time you get that large of a number, you are going to have all kinds of potential. And it doesn't matter contractors or government, both of them," she said.