South Korea’s top financial watchdog on Tuesday launched an on-site inspection of NHN’s mobile payment service Payco after news that its signature key was leaked broke the day before. This key is a tool that app developers use when registering and distributing their apps on app stores. It certifies that an app is developed by a certified company—in this case, Payco. Apps that used this signature key are considered safe and not detected as malicious by security programs. Back