The Chinese state has hacked the Ministry of Defence, Sky News understands.
MPs will be told on Tuesday of a massive data breach involving the MoD, targeting service personnel.
It is understood investigations have not shown any data has been taken.
The government will not name the country involved, but Sky News understands this to be China.
The Chinese state is to be accused of two or three attempts at hacking MoD employees – including personnel.
The cyberattack was on a payroll system with current service personnel, some officials and some veterans. It is largely names and bank details that have been exposed.
All salaries will be paid this month.
The contractor system is not connected to the main MoD computer systems and has been taken down with a review launched.
The MoD has been working at speed over the last 72 hours to understand the scale of the hack, after it was discovered in recent days.
This could raise questions about whether other countries with challenging relationships with China will want to share sensitive intelligence with the UK.
This comes fewer than two months after China’s “state-affiliated actors” have been blamed by the government for two “malicious” cyberattack campaigns in the UK.
Making a speech in the Commons, Deputy Prime Minister Oliver Dowden revealed the two incidents involved an attack on the Electoral Commission – responsible for overseeing elections and political finance – in 2021, and targeted attacks against China-sceptic MPs.
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