South Korean police raided the headquarters of Coupang Inc, the country’s largest e-commerce company, searching for evidence related to a historic data breach that compromised the personal information of more than 30 million people.

Police said they were looking for evidence that could help them determine how the breach took place as well as the personal information of the hacker, Yonhap News reported, citing officials. Coupang didn’t immediately respond to a request for comment about the raid.

Coupang’s data was breached during a months-long effort that circumvented its cybersecurity systems, officials have said. Nearly two-thirds of Koreans were affected, with researchers saying the country is on track to have suffered its highest number of cyberattacks to date this year.

While South Korea has endured major hacks in the past, Coupang’s data breach has riled consumers who rely on the service every day — from early morning breakfast deliveries to groceries.

Last week, President Lee Jae Myung said it was “truly astonishing” that Coupang had failed to detect unauthorized access of its systems for five months and South Korean lawmakers grilled Park Dae-jun, the online retailer’s chief executive officer, for hours about how the breach happened.

Lee’s chief of staff Kang Hoon-sik called on Monday for urgent action to prevent the leaked Coupang data from being used to carry out online fraud or unauthorized card transactions.