Details have not been made public until now to protect operational security, officials say.
The UK had long worked with Ukraine on cyber defence but shifted to providing direct help after the invasion, it has emerged.
Support is provided through the FCDO, with officials saying it has led the way amongst allies in providing specialist expertise. In some cases, there were attempts to knock ministries and infrastructure offline. But Russia did not initially appear to try and destroy telecommunications and energy sector networks, most likely because they were hoping to utilise them for their own purposes and "live off the land", according to one person involved.
In the early months of the war, the teams supported by the UK are also said to have seen specific Russian targeting of databases looking for personal identifiable information at the village, district and city level, which may have been Russian intelligence services seeking to identify and locate officials.
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