A watchdog is probing a cyber-attack on a council which is still unable to provide any online services more than a week after its systems were crippled.
Redcar and Cleveland Borough Council's website and all computers at the authority were attacked last Saturday, affecting 135,000 residents.
One expert said it looked like a ransomware attack, where files are scrambled until a ransom is paid.
The council notified the Information Commissioner's Office (ICO).
The watchdog said the authority had "made us aware of an incident and we are assessing the information".
The National Crime Agency said it was supporting the council, which has refused to confirm the nature of the hack.
Online appointment bookings, planning documents, social care advice and council housing complaints systems are just some of the services currently offline.
A team of experts from the UK's National Cyber Security Centre (NCSC) has been on site since the attack at 11:00 GMT on 9 February.
Council leader Mary Lanigan said "systems are being rebuilt" and they had "a massive team here - including cyber-security experts - working around the clock flat out to get it fixed".
The council said: "We are still able to receive and answer limited calls and emails and we will be prioritising urgent messages.
"There may be a slight delay in dealing with non-urgent calls and messages as the council's website is currently down.
"Our teams are working hard to resolve the problem and we would like to thank residents for their continued patience at this time."
Security researcher Kevin Beaumont said: "It seems almost certain they have suffered a severe ransomware incident.
"The serious nature of the attack and the impact it has had should raise eyebrows with UK authorities about the need to put more resources into tackling cyber-crime groups."