Elon Musk has subpoenaed a Twitter Inc. whistleblower, seeking documents and communications on the company's spam and alleged security vulnerabilities as the billionaire battles to end his agreement to buy Twitter for $44 billion, according to a court filing on Monday.

Musk sought information from whistleblower Peiter Zatko mostly about the way Twitter measures spam accounts. Musk has said he is walking away from the his deal for the company because Twitter misled him and regulators about the true number of spam or bot accounts on the microblogging platform.

But Musk also sought documents and communications about alleged attempts to hide security weaknesses and "Twitter's engagement in any unlawful activity."

A spokesman for Twitter did not immediately respond to a request for comment.

A famed hacker widely known as "Mudge," Zatko ended a stint as the head of Twitter's security earlier this year, and said in his whistleblower complaint that became public last week that the company falsely claimed it had a solid security plan.

A Twitter attorney said at a court hearing last week that Musk's focus on spam as a way to end his agreement to buy the company was "legally irrelevant" because Twitter always said its spam counts were only estimates, not binding representations.

The two sides have sued each other and are heading to a five-day trial on Oct. 17. Musk wants out of the deal and Twitter is asking Chancellor Kathaleen McCormick of the Delaware Court of Chancery to order him to buy the company for the agreed $54.20 per share.

Twitter's stock was down slightly at $40.36 on Monday morning in New York.