Imagine this. You're catching up on some emails. Verifying your identity with a passport picture. Paying an invoice with your bank details. In the background, a "bad actor" is collecting all of your encrypted emails. For now, that data is just an indecipherable jumble of letters and numbers. But the person harvesting it is patient. They're waiting for something called "Q-Day" to arrive. That's the day a quantum computer will be powerful enough to uncover not only your online data, but classified documents and spy secrets. "Right now encryption is protecting this data," Sushmita Ruj, associate professor at the University of New South Wales' Institute for Cybersecurity, says. "But what if a computer comes in later that decrypts everything? It becomes a real catastrophe." And depending on who you ask, Q-Day is right around the corner. The algorithm that changed everything This digital doomsday situation was set in motion in 1994, when a computer scientist called Peter Shor came up with a radical idea. Professor Shor gave a talk at the famous Bell Labs in New Jersey on how a quantum computer could solve a maths problem much faster than a regular computer. Somewhere along the way, his talk got misinterpreted. People started to assume he had solved a much larger maths problem called factoring. When Professor Shor gave his talk, he hadn't. But by the time the rumour mill caught up with him a few days later, he had. It was a huge deal, but it takes some maths to understand... Factors are pairs of numbers that divide another number evenly without remainders. Take the number 77. Its factors are seven and 11. You could guess the factors of 77 even without using a calculator. But when the number gets big - potentially thousands of digits long - it