Hackers can hide computer viruses in online video subtitles and use them to take control of computers, security experts have warned.

The attacks are embedded within the subtitle files that accompany many illegally downloaded films, and easily bypass security software and antivirus programs designed to keep computers safe.

Check Point, the security group that discovered the flaw, said millions of people who use video software including to stream or play films and TV shows on computers could be at risk.

They warned that the attack lets hackers take "complete control" over any type of device using the software, including smart TVs. It identified four programs - VLC, Kodi, Popcorn Time and Stremio - but said there could be more.