Why it matters: Former National Security Agency contractor Harold Martin was sentenced on Friday after what is likely to be the longest running breach of U.S. classified information the country has ever seen. Following 20 years of smuggling out files and information from his job at the NSA, Mr. Martin has been given nine years in jail.

Readers of this site are more likely than most to appreciate just how much data 50 terabytes is. That's the amount of data investigators discovered had been pilfered by Harold Martin, a former contractor who had worked for the National Security Agency (NSA) and other security services. And that's just the electronically-stored information -- Martin also had stacks of hard-copy files and documents, all kept in his Baltimore home.

The data comprised information on the United States' offensive cyber capabilities, spying methods, foreign cyber threats, and details of the NSA's own communications infrastructure. Prosecutors in his case say that they had no proof Martin shared the information with any adversarial powers, but if he had, it would have been a veritable gold mine.

Harold Martin pleaded guilty during his hearing in March this year, and on Friday was sentenced to nine years in prison, followed by three years of supervised release. As he has been in prison since his arrest in 2016, his three years already served will count as part of his overall sentence, which was handed down by District Judge Richard Bennett.

Martin's defense had portrayed him as a hoarder rather than a traitor. Without evidence that he had supplied the information to anyone, the charges were limited to 'willful retention of national defense information.'

Perhaps the most shocking aspect of this story is just how long Martin got away with his behavior. He first started gathering information and taking it home in 1996, and it wasn't until 2016 that he was arrested.

Interestingly, at the time of his arrest Martin was working for Booz Allen Hamilton -- the same agency that employed another infamous NSA contractor, Edward Snowden, though there is no other connection between the two.