June 21 (Reuters) - A group of hackers claiming

responsibility for a cyberattack on CDK's software systems has

demanded millions of dollars in ransom to put an end to the

hack, which affected auto dealers 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 cited people

familiar with the matter.

The auto retail technology and software provider planned to

pay the ransom, Bloomberg News reported.

CDK, which provides software to car dealerships, did not

immediately respond to a Reuters request for comment.

U.S. auto retailers Sonic Automotive ( SAH ) and Penske

Automotive ( PAG ) flagged a hit to their operations on Friday,

as CDK experienced a third consecutive day of outage.

In an emailed statement, Ford said that there was an

industrywide system outage for dealers who use CDK.

"However, many Ford and Lincoln customers are able to

receive sales and service support due to alternative processes

available to our dealers," Ford said.

Sonic said its dealerships were open and it was working to

minimize the disruption. The company said it was unable to

determine if the outage would affect its financial condition,

but that it did have a "negative impact" on its operations.

Penske said its Premier Truck Group business, which sells

new and used commercial trucks, also uses CDK's disrupted dealer

management system.

"Premier Truck Group has implemented its business continuity

response plans and continues to operate at all locations through

manual or alternate processes," Penske said.

The commercial truck dealership business has lower unit

volumes than Penske's automotive dealership business, which does

not rely on CDK's software.

Separately, Kia America told Reuters it was working with

affected dealers to reduce the impact of the outage and continue

towards "business as usual".

CDK on its website says it works with more than 15,000

retail locations across North America.