Las Vegas Sands is working with law enforcement to investigate the breach of its websites, which remain down a day after they were hacked.
State gambling regulators were investigating the cyberattack Wednesday, and the FBI also is aware of the matter.
Sands has added a new message to the hacked sites. The company's corporate site, as well as the home pages of the Venetian and Palazzo casinos, displayed a screen saying the sites are down for maintenance and providing phone numbers for all Sands properties. The hacking disrupted Sands' email systems.
Sands spokesman Ron Reese couldn't say whether credit-card records had been breached.
Sands runs the largest casino in the world, in the Chinese gambling enclave in Macau. It also owns hotel-casinos in Singapore and Bethlehem, Pennsylvania.
Explore further: World's richest casino exec opposes online wagers