The FBI says it is investigating a report that millions of American driver’s licenses were exposed online.

On Tuesday, the independent journalist Brian Krebs said he had discovered a dark web site selling digital scans of millions of driver’s licenses from people in the U.S. and Canada. He said he confirmed the authenticity of the data being sold with nine people.

In a brief statement issued on Wednesday, the bureau said it was “looking into the incident” but could not comment “due to the ongoing nature of the investigation.”

Krebs said he was alerted to the site after it was advertised on a Russian cybercrime forum, with his own driver’s license being offered as a free sample. Krebs said the service, dubbed Nexus, claimed to have tens of millions of licenses for people in the U.S. and Canada, as well as millions of other identification cards and travel documents and hundreds of thousands of medical records.

Krebs said the site vanished shortly after he published his investigation.

(Reporting by Raphael Satter, Editing by Franklin Paul and David Gregorio)