Indian online restaurant guide Zomato says hackers have the stolen data of more than 17 million users.
Email addresses and passwords were among the records stolen by hackers, Zomato said in a statement on its website.
"No payment information or credit card data has been stolen/leaked," Zomato said, adding that all affected accounts had been reset and it was working to plug any more security gaps in its systems.
The hashed passwords could not be decrypted back to plain text, Zomato said, but it nevertheless encouraged users who used the same password for other services to change it.
Zomato's statement came a day after the internet security website HackRead reported that a vendor who claimed to have hacked Zomato was selling the data of 17 million of its users on the "dark web."
Founded as a restaurant search service by Deepinder Goyal and Pankaj Chaddah in 2008, Zomato has more than 120 million users and operates in 23 countries including Australia, the United States, Portugal, Britain and Chile.