Video conference calls on platforms like Zoom are being hijacked and used to broadcast pornographic images or threaten the people inside them, the FBI has warned.

Such group video chats are being used to teach school classes and hold sensitive meetings but are being attacked by unknown people, authorities said.

The FBI shared stories of unknown people joining conference calls that were being used to teach school classes, before shouting profanities or using threatening language and then leaving.

It cautioned that people should make meetings as private as possible and take other precautions to ensure that only people invited to a call are able to get into it.

The phenomenon, colloquially known as “Zoom-bombing”, is not new. But more reports are emerging as people are forced to work and study from home over such video-teleconferencing (VTC) platforms because of the coronavirus crisis.

“The FBI has received multiple reports of conferences being disrupted by pornographic and/or hate images and threatening language,” the Boston division of the FBI warned in a statement on its website.

It highlighted two stories that happened at schools in the Massachusetts area, both of which saw unknown people attack school lessons that were being conducted on Zoom. Both happened in March, as the coronavirus crisis grew, the FBI said.

In one, an unidentified person joined a class and shouted a profanity and yelled out the teacher’s home address, the FBI said. In another, a person joined and was visible on the camera and could be seen with swastika tattoos, the FBI said.

It warned that people should not make meetings or classrooms public when they are being hosted on Zoom. Such chats can be restricted either by requiring a password or using the waiting room feature to only let in approved people.

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The FBI also warned people not to post a link to a given chat on any public platform. Instead, those links should be sent directly to the people involved.