A cyber-attack on a council’s computer systems is estimated to have cost more than £10m.
About 135,000 people were without online public services after Redcar and Cleveland’s website and computers were targeted in February.
The local authority has been in discussions with the government over covering the cost of the attack.
It said it had made “improvements” to its cyber-defences “with further upgrades planned”.
The council, which has been under pressure to reveal the cost of the incident, gave the figure in a budget update report.
Online appointment bookings, planning documents, social care advice and council housing complaints systems were among services knocked offline and experts from the UK’s National Cyber Security Centre (NCSC) were drafted in to help restore them.
Councillor Glyn Nightingale, cabinet member for resources and leader of the Liberal Democrat group, said the attack and the coronavirus outbreak had been “unprecedented” in their effects.
“These were two completely different sources of disruption to the council’s activities and services and came with serious consequences,” Mr Nightingale said.
A figure of £10.4m has been given to the government along with other information to assist with a due diligence process.
It has agreed to provide support to the council, according to the budget report.
Extensive recovery or replacement work to the IT infrastructure and systems made up £2.4m of the overall cost, the Local Democracy Reporting Service said.
The cost to individual departments amounted to £3.4m, while computer systems being out of action led to a reduction in enforcement income and lower collection levels for council tax and business rates and caused a further £1m impact, the council said.
The report said that at the time of the attack the council had industry standard tools deployed to secure its computer network, which had been configured to provide optimum protection.
Upgrades to its systems since February and enrolment on an NCSC scheme mean its cyber-defences “will be far more advanced than most peers in local government”, it added.
The attack continues to be subject to a criminal investigation.