Councils have been hit by at least 263 million cyber-attacks in the first half of this year - the equivalent of 800 every hour - new research has revealed.
A freedom of information request by Gallagher found nearly half (49%) of councils have been targeted since the start of 2017.
However, more than 200 councils either refused to answer the request on security grounds or did not respond, so Gallagher warned the number of attacks could exceed 500 million for this year alone.
The average cost of a successful attack on a council was £430,000, with one council reporting a loss of over £2m.
Tim Devine, managing director of public sector & education at Gallagher, said: ‘Councils are facing an unprecedented number of cyber-attacks on a daily basis. While the majority of these are fended off, it only takes one to get through to cause a significant financial deficit, a cost which the tax payer will ultimately foot.’
The research also found only 13% of councils currently hold a cyber-insurance policy to protect them from a financial loss or loss of data.
Mr Devine added: ‘Costs and reputational damage at this scale can be devastating for public authorities, many of which are already facing stretched budgets. In many scenarios, the people responsible for purchasing cyber insurance products need decisions to be made at member, or management level.’