An email virus contaminated some Peterborough City Council computers and prevented staff from using them.
The issue arose when a Microsoft Outlook email attachment, which appeared to be an invoice, was opened. The incident in October 2016, which has just been revealed, did not see any data stolen according to a council spokeswoman.
She added: “The matter was contained well in this situation and the council was able to operate with little disruption, if any, to services.”
The council is proposing to spend £796,000 more on ICT in its 2017/18 budget, with some of the money spent on preventing future attacks.