The cyber crime group that hacked into the customer service database of telecoms firm Odido and stole private details from millions of current and former clients has published some of the data on the dark web, broadcaster RTL reported on Thursday.

Odido refused to pay a ransom for the information and the hacker group, known as Shinyhunters, is now threatening a further release in 16 days’ time, RTL said.

Odido says data relating to 6.2 million clients was stolen in the hack, while the hackers claim more than 10 million customers are involved.

The information published on Thursday includes 275,000 bank account numbers, which are popular with cyber crime gangs for use in a wide range of financial fraud, RTL said.

In total, the hackers have released details relating to 430,000 people and 290,000 companies, including names, addresses, phone numbers, email addresses, bank account numbers and comments from customer service staff about particular clients.

That information included details about client deaths and health which had been collected, plus notes about unpaid bills and aggression. 

Odido said it had discussed what action to take with cybersecurity advisers and government officials. “Odido has decided not to negotiate with these criminals and not to be blackmailed by them,” the company said in a statement.

There is no legal way for Odido customers to find out if their own information has been published, RTL said.