At one point in Hillary Clinton’s slightly less than marathon press conference on Tuesday, the former secretary of state insisted that there were no security breaches of her personal “homebrew” email server. How could she possibly know this? The secretary of state’s emails represent a high-value target for cyber hackers operating out of foreign intelligence agencies, and a breach is unlikely to leave a trace of any activity that the layman or even a cyber-intelligence professional would notice. Just ask the State Department.

“Overlooked in the controversy over Hillary Clinton’s use of a private email server, is the fact that suspected Russian hackers have bedeviled State Department’s email system for much of the past year and continue to pose problems for technicians trying to eradicate the intrusion,” CNN reported on Tuesday.

As a matter of fact, the State Department is currently investigating what federal law enforcing officials are characterizing as the “worst ever” cyber-attack on America’s diplomatic establishment. “The attackers who breached State are also believed to be behind hacks on the White House’s email system, and against several other federal agencies, the officials say,” the CNN report continued.

Russian hackers, likely working for the Russian government, are suspected in the State Department hack.

The FBI has been investigating the hacking activity.

In part because of the Russian attack on State, U.S. intelligence officials have increased their warnings about Russian hacking activity in the U.S.

This report noted that even the State Department’s .gov addresses are not entirely secure, and that attacks on unclassified email systems can expose sensitive information to foreign intelligence services. Capture enough sensitive information, and a competent espionage service can piece together classified material. This is not an inconsequential matter.

We know as a result of the infamous Romanian hacker “Guccifer” that Clinton received messages from her longtime private advisor Sydney Blumenthal via email. How do we know? Blumenthal’s emails were compromised, and that hack revealed that he had shared a variety of private intelligence assessments as well as personal communications with Clinton while she served as the nation’s chief diplomat. It’s possible that none of the emails Clinton provided to the State Department included her correspondence with Blumenthal, according to a FOIA request from Gawker.

“The Clinton camp’s claims about the email account being above-board is also contradicted by the State Department’s response to Gawker’s inquires two years ago,” Gawker’s J.K. Trotter observed. “[T]he State Department replied to our request by saying that, after an extensive search, it could find no records responsive to our request.”

That is not to say that they found the emails and refused to release them—it is conceivable, after all, that the State Department might have attempted to deny the release of the Clinton-Blumenthal correspondence on grounds of national security or Blumenthal’s own privacy. Instead, the State Department confirmed that it didn’t have the emails at all.

Which is exactly why Clinton used a non-State Department email server to conduct her official business.

Without having access to those emails and the metadata associated with them, there is no way to confirm that Clinton’s emails remained secure from the private hacker who was almost certainly trying to access her email account. That is to say nothing of Russia or Chinese intelligence services.