The supermarket - which has 130,000 workers - emailed employees to inform them of the data theft and publication of the payroll system, while staff were also informed in person at branches. Details were also sent on a disc to a newspaper.
A spokesman said: "There has been no loss of customer data and no colleague will be left financially disadvantaged.
"We have already informed our colleagues about the theft and we are helping them take the appropriate actions to safeguard their personal data."
A review of the company's internal data security measures has been launched.
Detective Chief Inspector Nick Wallen of West Yorkshire Police said: "We are supporting Morrisons and their investigation into these matters."