Foreign spies are using online networking sites to target thousands of Government officials, high-tech businesses and academics, the head of MI5 has warned.

The Security Service’s director general, Ken McCallum, said more than 10,000 “disguised approaches” had been made by agents seeking to build relationships with their targets.

The Government warned that fake profiles were being created on sites including LinkedIn and Facebook on an “industrial scale”, with many being used as a ruse in an attempt to gain information relating to national security.

The Government’s Centre for the Protection of National Infrastructure has launched a new app aimed at preventing people from being duped by fake accounts.

Mr McCallum said: “MI5 has seen over 10,000 disguised approaches on professional networking sites from foreign spies to people up and down the UK.

“Foreign spies are actively working to build relationships with those working in Government, in high-tech business and in academia.”

He said the Think Before You Link app helps those who may be receiving disguised approaches to conduct their own “digital due diligence” checks before accepting unknown contacts online.

Current and former civil servants can be attractive targets because of their experience.

The app will boost the support and advice which Government staff, particularly those working on sensitive policy, already receive.

Chancellor of the Duchy of Lancaster, Steve Barclay, the minister responsible for cyber security, said: “The online threat via social media is increasing, with fake profiles on sites such as LinkedIn and Facebook being created on an industrial scale.

“Many of these profiles are established as an elaborate ruse for eliciting details from either officials or members of the public who may have access to information relating to our national security.

“It is therefore crucial that we do all we can to protect ourselves and our information, ensuring those who we connect with online are who they say they are. This new app will be an important tool in that endeavour.”

Officials pointed to a report from LinkedIn which showed 11.6 million fake accounts were stopped at the registration stage in the first six months of 2021.

The site, widely used by professionals as a networking tool, bans fake profiles and requires that members “are real people who represent themselves accurately and contribute authentically”.

A spokesperson for LinkedIn said: “Our Threat Intelligence team actively seeks out signs of state sponsored activity and removes fake accounts using information we uncover, and intelligence from a variety of sources, including government agencies.

“Our Transparency Report sets out the actions that we take to keep LinkedIn a safe place where real people can connect with professionals they know and trust, including that 97% of the fake accounts we removed were blocked at registration.

“We welcome the continued efforts in the UK of the Centre for the Protection of National Infrastructure.”