Over 10,000 government and public sector workers targeted by hostile states on social media, warns MI5

Fake profiles on networking and social media sites are being used on "an industrial scale" by rogue states and organised criminals, the UK's top domestic spymaster has warned.

Ken McCallum, director general of MI5, has issued the warning as a new campaign is launched to raise awareness of the threat.

Think Before You Link is primarily aimed at people who have access to classified or sensitive information, but is applicable to anyone in the private and public sector.

MI5 estimates that more than 10,000 UK nationals across virtually all government departments and key industries have been approached by malicious profiles on behalf of hostile states over the past five years. That is believed to be a conservative estimate.

"Malicious profiles on professional networking sites are being utilised on an industrial scale," said Mr McCallum.

"This campaign, which harnesses the insight derived from our intelligence, behavioural science experts and co-operation of 5EYES partners, will strengthen the UK's collective defences against this activity.

"Collaboration with the private sector has been key to this campaign - it highlights the immense value of combining our expertise and I hope it will form the blueprint for mutual partnerships in the future."

The campaign has been devised by the Centre for the Protection of National Infrastructure and is encouraging users of networking sites such as LinkedIn, and social media sites, to report any suspicious activity.

In recent years hostile states, such as China and Russia, have used social media websites to befriend or link to Britons working in government and other sensitive areas.

By creating fake profiles and posing as innocent contacts, they have sought to steal data and national security information.

The Think Before You Link initiative has also been adopted by the UK's 5Eyes intelligence partners - the US, Canada, Australia and New Zealand.

"Hostile foreign intelligence services are trying to steal our secrets and undermine our sovereignty," said Mike Burgess of the Australian Security Intelligence Organisation.

"Australians with access to sensitive information are being targeted online.

"Hostile foreign intelligence agencies have always sought access to personal information because they want to cultivate and recruit potential targets as sources," he said.

"In the past, attempted recruitment was time-intensive, experience and risky because foreign intelligence officers would need to operate on-location and in-person.

"Now, they can use the internet to work from the safety of their overseas headquarters, sending thousands of friend and networking requests with the click of a mouse."

Alan Kohler, assistant director of the FBI's counterintelligence division added: "Those state actors must now contend with the efforts of five united countries working in partnership to combat their hostile actions."