MGM Resorts said in a statement Monday that it had “recently identified a cybersecurity issue affecting some of the Company’s systems.” The issue was not described, but the statement said efforts to protect data included “shutting down certain systems.” It said the investigation was continuing. By Monday evening, the websites for all MGM Resorts International were offline with only a post offering telephone contacts for the various resorts’ locations.

According to reports on social media, the outages have impacted ATM cash dispensers and slot machines at MGM’s Las Vegas casinos, and that credit card machines were not functional at property restaurants. Some guests reported that they could not charge anything to their rooms and are unable to use their digital room keys.

The incident began Sunday but the extent of its effect on reservation systems and casino floors in Las Vegas and states including Maryland, Massachusetts, Michigan, Mississippi, New Jersey, New York and Ohio was not immediately known, company spokesman Brian Ahern said.

MGM Resorts International manages several Las Vegas properties, including Aria, Bellagio, The Cosmopolitan of Las Vegas, Delano Las Vegas, Excalibur, Luxor, Mandalay Bay, MGM Grand Las Vegas, New York-New York, Park MGM, and Vdara.

It also operates properties in China and Macau.