Data stolen from Hackney Council in a cyber attack last year has been published on the dark web, officials have said.
Experts supporting the east London council said a limited set of data had been put online but was not on a widely available on a public forum or visible through internet search engines.
Mayor of Hackney Philip Glanville said the council is working with the National Cyber Security Centre (NCSC), National Crime Agency (NCA), Information Commissioner’s Office (ICO) and the Metropolitan Police to establish what had been published and take immediate action where necessary.
The council said it appears at this stage that the vast majority of sensitive or personal information it holds has been unaffected.
Mr Glanville said in a statement: “It is utterly deplorable that organised criminals chose last year to deliberately attack Hackney, damaging services and stealing from our borough, our staff, and our residents in this way, and all while we were in the middle of responding to a global pandemic.
“Now, four months on, at the start of a new year and as we are all responding to the second wave, they have decided to compound that attack and now release stolen data.
“Working with our partners, we will do everything we can to help bring them to justice.”
The cyber attack in October took many of the council’s online services offline.
Mr Glanville apologised to residents for the concern the incident had caused and confirmed that anyone affected would be contacted directly.
“I fully understand and share the concern of residents and staff about any risk to their personal data, and we are working as quickly as possible with our partners to assess the data and take action, including informing people who are affected,” he said.
“While we believe this publication will not directly affect the vast majority of Hackney’s residents and businesses, that can feel like cold comfort, and we are sorry for the worry and upset this will cause them.
“We are already working closely with the police and other partners to assess any immediate actions we need to take, and will share further information about the additional action we will be taking as soon as we can.”