Payroll information on 1,000 personnel at a technology maintenance division of HP was emailed to a third party on Oct. 6.
It is believed the incident was caused by human error, but it is unclear why the person did not follow procedures in place to prevent these sorts of outcomes.
No other workers outside of HP Customer Delivery Services were affected. HP contacted staff to let them know what happened.
The payroll info contained National Insurance numbers, addresses and salaries.