An unknown number of names, along with contact and booking information, have fallen into the wrong hands, according to the booking site.
"When we discovered this, we took measures to limit the damage," the company said in a statement.
Booking has informed customers affected by the breach. It has not said how many were affected.
The company, headquartered in Amsterdam, lists more than 30 million accommodations around the world and says it provides experiences, transportation and accommodations to “millions of travelers.”
