Data stolen from Hackney LBC in a cyber attack has been published online by the criminals responsible.
The ‘serious cyber attack' last year affected the council's IT systems and services.
Experts supporting the council said the data was not visible through search engines or on any widely available public forum.
Hackney mayor Philip Glanville said: ‘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 council is working with the police and other organisations to determine what data has been published, and will support those affected by the crime.