Facebook users are being warned about a rise in so-called ‘malicious tagging’ scams designed to infect their phones, tablets and computers.

Over the past week, security researchers have spotted at least two ‘tag campaigns’ that were able to infect around 55,000 users a day.

The scams work by tagging no more than 20 friends of the victim in a malicious post designed to lure the friends into clicking a link or watching a video.

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Over the past week, security researchers have spotted at least two ‘tag campaigns’ which have infected more than 115,000 users.The scam works by tagging no more than 20 friends of the victim in a malicious post designed to lure people into clicking a link or watching a video (pictured)

Romania-based threat analyst Bogdan Botezatu, from security firm Bitdefender, reported on the first scam on 26 January.

In a blog post, Mr Botezatu said: ‘The scam starts with an alleged video in which a number of friends are tagged in.

'The number of tagged friends is always 20 but the alleged video is always different.'

HOW THE MAGNET SCAM WORKS The scam starts with an alleged video that is posted with 20 friends tagged. The number of tagged friends is always 20 but the alleged video is always different. Typically, the so-called video shows the goo.gl host underneath. This is a URL shortening service and not a video hosting site. After a victim clicks on this particular link, they are prompted to update Adobe Flash Player, at which point the hacker can take control of a device and install other malicious files and viruses designed to steal personal information. Once infected, the victim inadvertently posts the link to their own newsfeed, tagging another 20 people. Users are being warned to be wary of clicking on links they are tagged in, and are encouraged to check with friends who have posted the link to check its safety. Antivirus software will also detect malicious files and installations. Advertisement

The video shows the goo.gl host underneath, which Mr Botezatu said should raise some flags with more experienced users, as it is a URL shortening service and not a video hosting site.

After a victim clicks on this particular link, they are prompted to update Adobe Flash Player, at which point the hacker can take control of a device and install other malicious files and viruses designed to steal personal information.

This could include accessing personal files to steal photos, or logging what keys are typed to steal login details and passwords.

Once infected, the victim inadvertently posts the link to their own Facebook newsfeed, tagging another 20 people, and so on.

Another scam, also spotted by Mr Botezatu targeted Spanish speakers specifically, but had the same outcome.

In just one hour, this scam infected more than 5,000 users.

At the weekend, security expert Mohammad Reza Faghani additionally posted details of a tagging Trojan.

He wrote: ‘The trojan tags the infected user's friends in an enticing post.

'Upon opening the post, the user will get a preview of a porn video which eventually stops and asks for downloading a (fake) Flash Player to continue the preview.'

During two days of monitoring, Mr Faghani found the malware infected more than 110,000 users and was rising.

He said that by only tagging 20 people each time, the malware is able to keep a relatively low profile, but has the potential to reach more people because friends of friends can see tagged posts, depending on a person’s privacy settings.

After a victim clicks on a particular link, they are prompted to update Adobe Flash Player, at which point the hacker can take control of a device and install other malicious files. Once infected, the victim inadvertently posts the link to their own Facebook newsfeed, tagging another 20 people, and so on

This scam has been dubbed ‘Magnet’ because it attracts and lures people to it.

Mr Faghani explained that the malware even has the potential to take over a person’s mouse and keyboard, in addition to their operating system.

Users are being warned to be wary of clicking on links they are tagged in, and are encouraged to check with friends who have posted the link to check its safety.