Chinese spies are posing as recruitment agents to trick UK government and military staff into disclosing state secrets, MI5 has warned.
In a joint warning issued in a bulletin by the Five Eyes alliance, made up of UK, US, Australia, Canada and New Zealand agencies, it warned undercover operatives are using legitimate sites including LinkedIn, Indeed and Upwork to advertise fake analyst jobs.
Applicants are then pressurised into revealing "non-public" information which can be used by the Chinese military intelligence service.
The Five Eyes bulletin warns China's spies "seek to acquire privileged military, political and economic intelligence that can provide China with a strategic and tactical advantage".
Workers who could be targeted range from security clearance holders to academics and think tank employees, it warned.
Security Minister Dan Jarvis said: "I urge all government and military personnel to follow the National Protective Security Authority's advice to spot signs of online targeting and avoid inadvertently compromising our security.
"We have taken robust action to defend our country and will continue to tackle hostile actions from a range of states including China. A number of recent cases show the strength of the powers we have to bring to justice those that undertake acts on behalf of a foreign state."
The Five Eyes bulletin says Chinese agents post fake job adverts online before sifting through applicants' CVs to identify candidates worth exploiting.
Virtual interviews are carried out to discover if they have access to key areas of interest, like government contacts of military activities.
The last stage sees job hopefuls asked to write trial reports on topics including China's international relations or defence.
Recruits are then paid up to a thousand dollars per report through payment platforms.
In November Jarvis said MI5 had identified two LinkedIn profiles being used on behalf of the Chinese Ministry of State Security (MSS).
They were named as Amanda Qiu and Shirly Shen. Simon Whelband, a researcher for Conservative MP Neil O'Brien said one of the accounts had contacted him.
He said the message was written in poor English and included a job offer.
O'Brien told the BBC: "If you were more junior, you don't know what you're looking for.
"You might think it's a genuine offer that's made to you on LinkedIn."
A £170m upgrade to encrypted technology used in government business was announced last year, as well as new protections from Chinese cybercrime.
In September a case involving two men accused of spying for China collapsed a week before it was due to go to trial.
The CPS said it fell apart because evidence could not be obtained from the government referring to China as a national security threat.
