Official documents critiquing security measures in advance of the Super Bowl were left on a commercial plane, CNN is reporting Monday.

The Department of Homeland Security documents critiqued the response to a simulated anthrax attack on Super Bowl Sunday. The December 2017 reports were marked "For Official Use Only" and "important for national security."

But a CNN employee discovered copies of them, along with other sensitive DHS material, in the seat-back pocket of a commercial plane. The reports were accompanied by the travel itinerary and boarding pass of the government scientist in charge of BioWatch, the DHS program that conducted the anthrax drills in preparation for Super Bowl LII in Minneapolis.

In an article on its website, CNN said it delayed publication of the breach.

"CNN decided to withhold publication of this article until after the Super Bowl after government officials voiced concerns that publishing it prior to the game could jeopardize security for the event. A DHS official told CNN that areas for improvement identified in the draft reports had been addressed prior to Sunday's game and that the agency had 'great confidence' in its preparedness.

CNN said thatDHS officials also argued that disclosure of some material contained in the draft reports could threaten national security, regardless of when it was published. "Based on that concern, CNN is withholding some details contained in the documents," the news outlet said.

Staff report