(CNN) A former National Security Agency contractor accused of the largest security breach in US intelligence history is expected to plead guilty on Thursday, his lawyer told CNN.

Harold "Hal" Martin, 54, had worked for 23 years as a contractor for companies that contracted with various intelligence agencies and maintained a government clearance throughout his career.

Prosecutors described him as a hoarder who took home a whopping 50 terabytes of files, including a number of classified ones he stored on drives in his home and car. They have not publicly accused him of trying to leak that information.

Martin's arraignment is scheduled for Thursday afternoon in Baltimore, where he will enter a guilty plea, Wyda told CNN. The details of his plea deal weren't immediately made clear.

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