Information relating to employees at Greater Manchester Police (GMP) was accessed when a company was targeted in a cyber attack.
The company, which according to the BBC is a third-party supplier of ID cards, holds information on a number of organisations across the UK.
Assistant Chief Constable Colin McFarlane, of GMP, said the cyber attack is being treated "extremely seriously".
ACC McFarlane said: "We are aware of a ransomware attack affecting a third-party supplier of various UK organisations, including GMP, which holds some information on those employed by GMP.
"At this stage, it’s not believed this data includes financial information.
"We understand how concerning this is for our employees so, as we work to understand any impact on GMP, we have contacted the Information Commissioners Office and are doing everything we can to ensure employees are kept informed, their questions are answered, and they feel supported.
"This is being treated extremely seriously, with a nationally-led criminal investigation into the attack."
This article was written by Jack Tooth. To contact him, email jack.tooth@newsquest.co.uk or follow @JTRTooth on Twitter.
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