Buzzfeed's courts and justice reporter Zoe Tillman is reporting on a secret grand jury proceeding in DC, but it's so secret no one knows what it's about.

Tillman first points to a Politico piece from October: "Mueller link seen in mystery grand jury appeal."

After detailing some court docs as background, Tillman tweets, "They’ve sealed not only the courtroom, but the whole floor." It's getting a lot of attention:

Politico senior reporter confirms:

Here's what some are saying:

Also, this from a Reuters justice reporter: