A decade-old internet scourge called ransomware went mainstream on Friday when cybercriminals seized control of computers around the world, from the delivery giant FedEx in the United States to Britain's public health system, universities in China and even Russia's powerful Interior Ministry. Ransomware is nothing new. For years, there have been stories of individuals or companies horrified that they have been locked out of their computers and that the only way back in is to pay a ransom to someone, somewhere who has managed to take control. But computer criminals are discovering that ransomware is the most effective way to make money in the shortest amount of time. Friday's attacks were a powerful escalation of earlier, much smaller episodes. Hackers exploited a vulnerability in Microsoft servers that was first discovered by the National Security Agency and then leaked online. It allowed the ransomware to spread [to] more than 70,000 organizations. There is even now a concept of "ransomware as a service" - a play on the Silicon Valley jargon "software as a service," which describes the delivery of software over the internet. Now anyone can visit a web page, generate a ransomware file with the click of a mouse, encrypt someone's systems and demand a ransom to restore access to the files. If the victim pays, the ransomware provider takes a cut of the payment. Ransomware criminals also have customer service lines that victims can call to get help paying a ransom.