Malicious software or "ransomware" has been used in a massive hacking attack, affecting tens of thousands of computers worldwide. Software security companies said a ransomware worm called "WannaCry" infected about 57,000 computer systems in 99 countries on Friday, with Russia, Ukraine, and Taiwan being the top targets. The hack forced British hospitals to turn away patients, affected Spanish companies such as Telefonica, and threw other government agencies and businesses into chaos. How it works: WannaCry is a form of ransomware that locks up files on your computer and encrypts them in a way that you cannot access them anymore. It targets Microsoft's widely used Windows operating system. When a system is infected, a pop-up window appears with instructions on how to pay a ransom amount of $300. The pop-up also features two countdown clocks; one showing a three-day deadline before the ransom amount doubles to $600; another showing a deadline