17 had the option to change or cancel their reservation free of charge. The website previously offered a list of phone numbers to call by property, but it was directing customers as of Wednesday afternoon to book show tickets via Ticketmaster and noted guests with check-in dates through Sept. The company's reservations system appears to be down, and the website directs customers to make reservations or contact a concierge. MGM Resorts is the largest casino operator in Las Vegas, where it has some of the best-known resorts on the Las Vegas Strip, including the MGM Grand, Bellagio, Cosmopolitan, Aria, Mandalay Bay, Luxor, New York-New York, Excalibur and Park MGM. The cyberattack is believed to affect properties in Nevada, Maryland, Massachusetts, Michigan, Mississippi, New Jersey, New York and Ohio. The issue first began Sunday, the Associated Press reported. on Monday faced a 'cybersecurity issue' that caused the gaming giant to temporarily shutter computer systems across the country. Various MGM Resorts International properties across the U.S.