Holiday Inn owner, Intercontinental Hotels Group, has confirmed the company has been hit by a cyber attack.
IHG, which has some of the world's largest hotel chains, issued a statement saying it was investigating "unauthorised access" to a number of its technology systems.
The UK-based company, which manages the Holiday Inn, Crowne Plaza and Regent hotels, said its "booking channels and other applications" had been disrupted since Monday.
"IHG is working to fully restore all systems as soon as possible," the company said.
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IHG confirmed it was assessing the nature, extent and impact of the incident and had implemented its response plans including appointing external specialists to investigate the breach.
The company is also in the process of notifying regulatory authorities.