They defended their practice of holding computers for ransom after the FBI took down a major ransomware group. Some of the most destructive ransomware hackers in the world appear to be on edge after the U.S. reportedly took down one of their colleagues. Several ransomware gangs posted lengthy anti-U.S. screeds, viewed by NBC News, on the dark web. In them, they defended their practice of hacking organizations and holding their computers for ransom. They appear prompted by the news, reported Thursday by Reuters, that the FBI had successfully hacked and taken down another major ransomware group called REvil....