Cyber attacks from Russia, China, Iran and North Korea pose "strategic national security threats to the UK", according to the CEO of the UK's National Cyber Security Center (NCSC).
Ciaran Martin also warned that "large-scale global cyber crime" was a threat to "our social fabric, our way of life and our economic prosperity", despite often being "low in sophistication".
Mr Martin made his comments in the foreword to NCSC's Annual Review, which details the group's accomplishments last year.
The NCSC, which is part of the GCHQ spy agency, claims to have "handled" 658 attacks on 900 organizations, including schools, airports and emergency services.
Mr Martin said many attacks were "from hostile nation states" but that he was unable to give even details about "operational successes".
On Monday, the NCSC published the results of a two-year investigation conducted with the US National Security Agency (NSA), which accused a group – known as Turla – of suspected links to Russian government attacks on multiple countries.
According to NCSC and NSA, Turla stole stolen Iranian tools and infrastructure to obscure its origins attacks.
The NCSC released some information about its domestic operations, including one that prevented hundreds of thousands of fraud cases by alerting banks to stolen credit cards being sold online.
Known as Operation Haulster, it collected stolen credit cards then reported them to banks – with the result that, NCSC claimed, "high-end cyber crime victims were protected before they lost a penny".
This Annual Report, the third since NCSC was founded in 2016, is the first to break down incidents by sectors.
The sector affected by most incidents was government, with academia in second place, followed by IT, managed service providers and – in fifth joint – health and transport.
Yet cybersecurity experts said 658 attacks were small compared to the number of cyber attacks launched each day, but differed on whether it was too low to be meaningful.
"Highly sophisticated attacks are using surgical precision, with near military levels of planning, preparation and execution," said Lewis Henderson, VP of Threat Intelligence at Glasswall Solutions Limited.
"This explains the relatively low volume of NCSC attacks that are defending … the avoidance of potentially catastrophic events cannot be downplayed."
Raef Meeuwisse, author of Cybersecurity for Beginners, disagreed.
"The general standard of cybersecurity deployed by most commercial enterprises and government functions in the UK continues to be woefully inadequate. However, if we were to believe this report from the NCSC, everything is coming together just fine," he said.
"This report appears to be a self-congratulatory pat on the back when cybercrime revenue continues to rise to new heights."
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