Kensington and Chelsea Council (KCC) has been fined £120,000 by the UK data watchdog for inadvertently identifying hundreds of property owners.
It gave the names and addresses of 943 people who owned vacant homes in the borough to journalists and three high-profile names were published by a national newspaper.
The story came out about six weeks after the Grenfell Tower fire which killed 71 people in June.
KCC has apologised for the error.
The fire on 14 June had thrust the issue of empty homes into the spotlight, with many people arguing they could be used to house displaced survivors.
The Information Commissioner's Office (ICO) said the council had committed a "serious contravention" of data protection and added in its report that such disclosures "required guidance and oversight" at a time when "the feeling of social inequality was running high in this wealthy borough".
'No Excel training'
Three journalists requested a break-down of all empty properties in the borough on 30 June under the Freedom of Information (FOI) Act.
The information was compiled in a pivot table - a type of Excel spreadsheet which hides underlying source data - in this case 943 names and addresses, from view.
But the ICO said in its report that "double-clicking on any cell would have revealed" the sensitive information contained in the document.
The commissioner found the council had not provided its FOI team "with any (or any adequate) training on the functionality" of Excel spreadsheets and had "no guidance for the FOI team to check spreadsheets" for hidden data.
The ICO first highlighted the issue in a 2013 blog after it fined two other public bodies for similar breaches resulting from the use of pivot tables.
KCC said: "It was an error and we apologise. We accept the fine, and we have reviewed our processes to prevent this happening again."