In a letter disclosed Monday in a federal court filing, the FBI confirms one of the world’s worst-kept secrets: It is looking into Hillary Clinton’s use of a private email server.

Why say this at all, since it was widely known to be true? Because in August in response to a judge’s direction, the State Department asked the FBI for information about what it was up to. Sorry, the FBI said at the time, we can neither confirm nor deny the existence of any investigation.

Now, in a letter dated February 2 and filed in court Monday, the FBI’s general counsel, James Baker, notes that in public statements and congressional testimony, the FBI “has acknowledged generally that it is working on matters related to former Secretary Clinton’s use of a private email server.”

Baker says the FBI has not, however, “publicly acknowledged the specific focus, scope or potential targets of any such proceedings.”

He ends the one-paragraph letter by saying that the FBI cannot say more “without adversely affecting on-going law enforcement efforts.”

The letter was filed in one of the Freedom of Information Act cases brought against the State Department over access to documents from Hillary Clinton’s time as secretary of state. This one was filed by Judicial Watch.