MGM Resorts International, the casino and hotel giant, acknowledged on Wednesday that it was the victim of a data breach last year, the latest company to have the personal information of its customers exposed.

MGM did not disclose the number of customers affected, but Under the Breach, a firm that monitors cybercrimes and provides intelligence about potential data breaches to companies, said 10.6 million people were affected.

Under the Breach said several high-profile guests at MGM properties had their email addresses, phone numbers and physical addresses exposed, including one guest with the same name as Jack Dorsey, Twitter’s chief executive.

Twitter declined to comment on Wednesday night.

MGM Resorts said the vast majority of those affected had “phone book information” breached such as name, phone number and address. About 1,300 individuals had more sensitive data — from their driver’s licenses, passports or military ID cards — exposed, MGM said.