Live Nation Entertainment said on Friday it was investigating a data breach at its Ticketmaster unit that it discovered on May 20, the latest in a string of high-profile corporate hacks in the past year.

In a filing with the U.S. Securities and Exchange Commission, Live Nation said it found “unauthorized activity” in a third-party cloud database that mainly contained Ticketmaster data, and was working with forensic investigators.

Last week a little-known cybercrime group named ShinyHunters said it had stolen user data of over 500 million Ticketmaster customers, according to various media reports.

Live Nation did not mention ShinyHunters in its SEC filing.

The company did not respond immediately to a Reuters request for comment.

The breach comes as the concert promoter has been battling regulatory scrutiny over antitrust concerns. Live Nation was hit last week with the first in a likely a wave of consumer antitrust lawsuits after the U.S. government and states sued to break up the firm, arguing that along with its Ticketmaster unit, the company was illegally inflating concert ticket prices.

Live Nation in its filing said that on May 27, “a criminal threat actor offered what it alleged to be company user data for sale via the dark web.”

“We are working to mitigate risk to our users and the Company, and have notified and are cooperating with law enforcement,” the company said. “As appropriate, we are also notifying regulatory authorities and users with respect to unauthorized access to personal information.”

The breach hasn’t had and is unlikely to have a material impact on Live Nation’s business or financials, the company said.

“We continue to evaluate the risks and our remediation efforts are ongoing,” Live Nation said.

(Reporting by Zeba Siddiqui in San Francisco; Editing by Leslie Adler)