June 24 (Reuters) - More U.S. auto dealers flagged a hit

from an outage of CDK's software system due to a cyber attack on

Monday as the company worked to restore systems used by over

15,000 retail locations across North America.

AutoNation ( AN ), a leading auto retailer in the U.S. said

the outage was disruptive and had adversely impacted its

business though its outlets remain open, continuing to sell,

service, and buy vehicles.

"As the incident is ongoing, the full scope, nature and

impact of the incident is not yet known," AutoNation ( AN ) said.

The company and peer Group 1 Automotive ( GPI ) said they

were using alternative processes such as manual paperwork to

conduct their business. Both said they had taken precautionary

steps to protect their data.

"The timing of the restoration of other impacted CDK

applications remains unclear at this time," Group 1 said in a

statement.

Bloomberg News reported on Friday that a group of hackers

claiming responsibility for the attack on CDK's software systems

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

hack.

Though auto retailers have not outlined any sales hit,

analysts have flagged a possible impact. "We note some potential

risk to late-June (U.S. auto sales) volume from the reported CDK

dealer disruptions," Citi analysts said in a note last week.

Auto retailer Sonic Automotive ( SAH ), last week, said the

CDK outage was likely to have a negative impact on its business

operations until the systems were fully restored.

Penske Automotive ( PAG ) said its Premier Truck Group

business had implemented business continuity plans in response

to the outage.