Boffins at the University of Michigan in the US and Zhejiang University in China have been looking into an unusual attack vector.

In a paper distributed via ArXiv, titled, "Private Eye: On the Limits of Textual Screen Peeking via Eyeglass Reflections in Video Conferencing," boffins Yan Long, Chen Yan, Shilin Xiao, Shivan Prasad, Wenyuan Xu, and Kevin Fu describe how they analyzed optical emanations from video screens that have been reflected in the lenses of glasses.

"Our work explores and characterizes the viable threat models based on optical attacks using multiframe super resolution techniques on sequences of video frames. Our models and experimental results in a controlled lab setting show it is possible to reconstruct and recognize with over 75 percent accuracy on-screen texts that have heights as small as 10 mm with a 720p webcam."

That corresponds to 28 pt, a font size commonly used for headings and small headlines.

While seeing the headlines is not the privacy and security problem of being able to read smaller 9 to 12 pt fonts things will get worse as high-resolution webcams become more common.

"4k cameras should peek at most header texts on almost all websites and some text documents," said Long.

This would enable bosses to see what subordinates were browsing in a video work meeting, to business and trading scenarios where the reflections might leak key negotiation-related information.

Zoom already provides a video filter in its Background and Effects settings menu that consists of reflection-blocking opaque cartoon glasses. Skype and Google Meet lack that defense.