Thousands of Ticketmaster users may have had their data compromised in a security breach.

Ticketmaster says it discovered unauthorized activity on an isolated cloud database hosted by a third-party data services provider between April 2 and May 18.

The company learned a few days later that some personal information of customers may have been affected, possibly including email, phone number, or encrypted credit-card information.

The Beverly Hills, California-based ticket sales giant says it’s working with authorities and cybersecurity experts, credit-card companies and banks in its investigation, and has found no further unauthorized activity.

Ticketmaster says it is reaching out by email or mail to customers it believes were affected.

The company is offering credit-monitoring services to customers in Canada and also recommends customers monitor their bank activity and emails to ensure there’s no suspicious activity.