(Reuters) – A group of hackers claiming responsibility for a cyberattack on CDK software systems have demanded a multimillion-dollar ransom to end a breach that hit car dealerships across the United States, Bloomberg News reported on Friday.

The group behind the attack is believed to be based in Eastern Europe, according to the report, which cites people familiar with the matter.

According to Bloomberg News, the supplier of automotive retail technology and software planned to pay the ransom.

CDK reported that it experienced a cyber incident on Wednesday.

While it did not comment directly on the Bloomberg report, in an emailed statement Saturday, the company said it had launched an expert investigation, notified law enforcement and began the process of restoring operations. CDK says restoration will take several days.

“…In the meantime, we continue to actively engage with our customers and provide them with alternative ways to conduct business,” CDK said in a statement.

On Friday, U.S. auto retailers Sonic Automotive (NYSE:) and Penske Automotive reported a decline in their business as CDK experienced a third straight day of outages.

In an emailed statement, Ford (NYSE:) said there was an industry-wide system outage at dealers using CDK.

“However, many Ford and Lincoln customers can obtain sales and service support through alternative processes available at our dealers,” Ford said.

Sonic said its dealerships are open and it is working to minimize disruptions. The company said it was unable to determine whether the outage would have an impact on its financial situation, but that it was having a “negative impact” on its business.

Penske said Premier Truck Group, which sells up-to-date and used commercial trucks, also uses the CDK dealer management system, which is experiencing disruptions.

“Premier Truck Group has implemented its business continuity response plans and continues to operate at all locations using manual or alternative processes,” Penske said.

The truck dealer business has a smaller unit count than Penske’s auto dealer business, which does not rely on CDK software.

Separately, Kia America told Reuters it is working with affected dealers to reduce the impact of the outage and continue normal operations.

CDK says on its website that it works with more than 15,000 retail locations in North America.