June 23 (Reuters) - Retail technology and software

provider CDK Global has begun working to restore systems used by

about 15,000 auto retailers to conduct day-to-day business,

Bloomberg News reported on Sunday.

The company expected the process to take "several days and

not weeks," the report added, citing an automated message sent

to customers on Sunday.

CDK did not immediately respond to request for comment

outside regular business hours.

Last week, a dealer who received a letter from CDK said

the company informed him it could take

several

more days to get the systems up and running.

The company, which provides software to car dealerships,

briefly shut down all its systems on Wednesday, saying it was

investigating

a cyber incident.

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.

Bloomberg had previously reported that 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.