A multi-day outage impacting the InterContinental Hotels Group (IHG) is due to "unauthorized activity."

The scale of the intrusion and whether customer data was impacted is not yet known.

IHG websites, apps, and services have been intermittently down since 9pm ET on Sunday, likely costing it hundreds of thousands in lost bookings.

The company owns 17 brands, including InterContinental Hotels & Resorts, Holiday Inn, Hotel Indigo, Crowne Plaza, and Regent Hotels & Resorts.

The company said that the "significant disruption" was down to unauthorized activity, but provided no further details about the apparent cyberattack. It is not clear if the incident is ransomware or a hack.

IHG said it had appointed external cybersecurity specialists to investigate the incident, and was notifying regulatory authorities. It added that its hotels were still operational - for those that could get a booking.

This article will be updated as we learn more.