Hacker group TheDarkOverlord claims to have stolen 18,000 documents from business insurer Hiscox and several other law firms involved in litigation surrounding the September 11 attacks. The hacker group, previously responsible for the theft of Netflix episodes and several other cyber-extortion attacks, is threatening release of the stolen documents unless a ransom is paid in Bitcoin.

In a statement posted to Pastebin, The Dark Overlord claimed the theft of “hundreds of gigabytes of litigation related documents,” including emails, voice mails, retainer agreements, non-disclosure agreements and communications between government bodies and Fortune 500 companies.

A spokesperson for the Hiscox Group confirmed details of a law firm breach to Motherboard, writing, “One of the cases the law firm handled for Hiscox and other insurers related to litigation arising from the events of 9/11, and we believe that information relating to this was stolen during that breach.”

The Dark Overlord group makes large claims for the stolen documents. “Edward Snowden leaks were quite impressive and caught the world’s attention due to the highly sensitive nature of the materials and the global impact. What we’re about to announce and leak will top Edward Snowden’s finest work, both in volume and in impact,” the document reads, describing it as the “most significant data breach ever to have occured.”

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