Washington, Mar 28 (IANS): A former National Security Agency (NSA) 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 lawyer, Jim Wyda, had previously argued in court that his client "isn't Edward Snowden" and followed "no system" or "spycraft" in taking home those files.

Martin's arraignment is scheduled for Thursday afternoon in Baltimore, where he will enter a guilty plea, Wyda told CNN on Wednesday.

The details of his plea deal weren't immediately made clear.

In 2017, Martin was arrested at his Maryland home and charged with 20 counts of stealing a host of classified files for years and across various jobs.

The files he stole, according to charging documents, included a number of NSA files, including reports on future plans, spy tools, and technical descriptions of an NSA communications programme.

While Martin is accused of being the most prolific of them, the NSA has experienced a number "insider threats" in recent years, in which agency employees and contractors have violated classification laws to remove agency files.

In 2014, Edward Snowden, who like Martin did NSA work through consulting firm Booz Allen Hamilton, famously stole more than a million pages of NSA documents which he gave to a handful of journalists in the name of exposing programs that exploited privacy. He has been charged with a violation of the Espionage Act and currently resides in Moscow.

In 2017, Nghia Pho, an employee with NSA's Tailored Access Operations, pleaded guilty to taking home classified work files for five years.

Also in 2017, Reality Winner, an analyst upset about scepticism that Russia had attempted to interfere with the 2016 US election, leaked raw NSA intelligence to the Intercept that showed an apparent effort by Russian military intelligence to hack US election systems.

Both Pho and Winner accepted a plea deals and are serving a five-year sentences.