As secretary of state, Hillary Clinton signed a nondisclosure agreement in which she acknowledged that classified information is classified regardless of whether it is “marked or unmarked” — a distinction which undermines one of the Democratic presidential candidate’s main defenses of her use of a home-brew email system.

Signers of the document, the existence of which the Washington Free Beacon reported on Friday, also agree that all information that they have access to “is now and will remain the property of, or under the control of the United States government unless and until otherwise determined by an authorized official or final ruling of a court of law.”

The “Classified Information Nondisclosure Agreement,” or SF-312, also makes clear that “classified information is marked or unmarked classified information, including oral communications.”

That poses two problems for Clinton, who signed the document on Jan. 22, 2009, a day after taking office.

Not only does nullify her claim that none of her emails contained information that was “marked” classified, it also calls into question her failure to turn over her work-related State Department emails to the agency in December, nearly two years after leaving office.

“I can only repeat what happens to be the case — that I did not send nor receive information that was marked classified at the time that it was sent or received,” Clinton said in September.

More than 600 of the Clinton emails that the State Department has released so far have been found to contained information that the agency says is currently classified. While both the Clinton campaign and the State Department assert that the information was not classified at the time it was originated, others have questioned the claim.

Many of the now-classified documents contain a type of information called foreign government information. As Reuters reported in August, the federal government considers such information, which comes from foreign officials, to be “born classified.”

The finding that Clinton signed the SF-312 settles a question that The Daily Caller raised in September. The State Department declined to comment on the matter at the time. (RELATED: State Department Is Mum On Whether Hillary Signed Important Classified Information Nondisclosure Agreement)

The Free Beacon also reported that Clinton signed another nondisclosure agreement pertaining to the handling of the most sensitive classified information.

By signing the “Sensitive Compartmented Information Nondisclosure Agreement,” Clinton agreed that she had been advised “that the unauthorized disclosure, unauthorized retention, or negligent handling of SCI by me could cause irreparable injury to the United States or be used to advantage by a foreign nation.”

That agreement pertains to the Clinton email scandal because of two emails she received on her personal email account that the intelligence community’s inspector general has determined contained “top secret/sensitive compartmented information,” or TS/CSI.

The discovery of those emails prompted the Justice Department to open an investigation. The FBI also seized Clinton’s server, which was being maintained at a data center in New Jersey.

Two of Clinton’s top State Department aides, Cheryl Mills and Huma Abedin, also signed that nondisclosure agreements. As with Clinton, both used off-the-books email accounts on which they sent and received classified information.

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