Denmark has suffered a major data breach after hackers gained access to the country’s national population registry, compromising the personal information of millions of people.

The country’s Minister for Digital Affairs announced the breach on Monday, describing it as “an extremely serious incident” that affected 8.8 million people.

“Unauthorised individuals obtained illegal access” to the names, addresses and CPR, including those who have died or emigrated, the ministry said in a press release, referring to Denmark’s social security numbers.

“This is an extremely serious incident,” Christina Egelund, digital affairs minister, was quoted as saying in the press release.

“Together with all the relevant authorities, we are in the process of mapping out the full extent of the incident,” she added.

Denmark has a population of about six million, but its national registry contains information on roughly 11 million people, including deceased individuals and those who have emigrated from the country.

An investigation has been launched into the breach, while authorities said they have yet to establish who was responsible.

According to the government, the hackers gained access to the registry by breaching a Danish company that was legally authorised to access the database.

The company’s access to the registry has not been revoked.