However, luckily, five students from Good Hope School, in Kowloon, have come up with a simple solution.
Concerned by the widespread problem, they have created an LCD monitor that can be read only by using a modified pair of glasses.
The girls' bright idea made the final eight of a competition organised by the Hong Kong Joint School Electronics and Computer Society. The winners were a group of six boys from King's College, in Mid-Levels, who had the idea for an application that helps the blind to "read" images and videos.
"Our product is not as practical as that of the winners," says Niko Man Pui-yi, a member of the Good Hope team. "We sincerely believe they deserved to win."
The team of Cherry Lee Suet-yee, Joyce Mok Wing-sze, Niko, Jasmine Chan Hiu-tsun and Rainbow Cheung Hiu-tung, took three months to research and produce their clever design.
At first they struggled to make their project work, but perseverance, painstaking research on the internet and in the library - and some good advice from their physics and information and communications technology teachers - paid off.
They found it hard to understand some of the jargon and technical details, but their teachers advised them to always go back to basics and build their design step by step.
The team decided polarisation - where a plastic sheet can allow some light waves to pass through it while blocking others - was the key to making their monitor safe from prying eyes.
They searched for discarded LCD monitors, which contain two polarisers, or filters, placed on top of each other - from relatives and friends.
"At the start, we kind of stared at the monitor for a while, wondering what to do with it," says Joyce. Finally they decided to physically tear it apart and get into its many layers. Slowly things began to come together as they fiddled and experimented with the different parts.
After destroying one monitor, they succeeded in creating three "invisible screens" from three separate monitors.
They admit their product is not perfect. When viewed from the side, at a certain angle, there's a faded image, even without using glasses. The group said this can be resolved by adding a privacy filter on the screen.
They say the hardest part of the competition was at the start - trying to choose what to design. "There was so much choice about what we could do," says Cherry. "Trying to decide on one topic required lots of time and patience."