Prosecutors said Andrew Skelton, 43, leaked the information in response to a warning he was given after the company found out he used the mail room at Morrison’s HQ in Bradford to send out eBay packages.
The data breach cost the company more than £2 million to rectify, Bradford Crown Court heard.
Data containing information including salaries, National Insurance numbers, dates of birth and bank account details were sent to The Guardian, Trinity Mirror Newspapers and the Bradford Telegraph & Argus last year, prosecutor Katherine Robinson told a jury today. It was also uploaded to data sharing websites.
Miss Robinson was opening the case against Skelton, a senior internal auditor at Morrisons at the time, who denies fraud and other offences.
She told the jury of seven women and five men how the defendant, of Water Street, Liverpool, was subjected to disciplinary action in 2013 after a package was found in the mail room at Morrisons HQ, in Bradford.
Miss Robinson said the initial suspicion was that the package contained controlled drugs but this was found not to be the case.
The prosecutor said Skelton told the internal investigator he had been conducting eBay deals using the HQ mail room and he was given a warning.
“He was allowed to continue with his employment,” Miss Robinson said.
“The prosecution case is that as a result of that disciplinary matter the defendant bore a grudge against Morrisons .... which led to his offending in this case.”
The jury heard how the police investigation into the data breach led to detectives discovering a draft resignation letter that Skelton has written around the time of the disciplinary matter.
She said this letter spoke of the “anger and frustration that had not diminished with the passage of time” and how he had “scant regard” for the firm.
Miss Robinson quoted from the letter, saying: “I have almost as little concern for the company as it does for me.”
Skelton sat alone in the dock wearing a dark suit with a white shirt and light grey tie. He has short, brown hair and wears glasses.
Skelton denies one count of fraud by abuse of position, one of unauthorised access to data with the intent of committing an offence and one of disclosing personal data..
The trial continues.