New York CNN  —  Live Nation said a hacker is offering alleged user data primarily from Ticketmaster for sale on the dark web in a regulatory filing Friday. Live Nation said it identified “unauthorized activity” on May 20 and launched a probe with forensic investigators into the potential hack. Live Nation is the parent company of Ticketmaster. The filing said the data went up for sale on May 27. Live Nation said it is working with law enforcement. “As appropriate, we are also notifying regulatory authorities and users with respect to unauthorized access to personal information,” the filing said. Live Nation said it does not believe the hack has had any financial or business operation impact. A group called ShinyHunters claimed responsibility for the hack, trade publications reported. Ticketmaster has not returned multiple requests for comment, and the filing did not confirm the scale of the hack. The potential hack adds to a tense year for the ticketing giant. Just last week, the US government and dozens of states sued Live Nation, alleging that for years Ticketmaster abused its industry dominance to harm fans nationwide.