The whole internet will shut down for 24 hours.
The dire forecast comes from the US technology security vendor LogRhythm. According to James Carder, the company's chief information security officer and vice president, it won't just be a technical issue stopping people from uploading their selfies on Instagram.
"In 2017, we're going to see it hit big sometime, somewhere," he said. "If the internet goes down, financial markets will tank."