I'm using the USBSerial_HelloWord and also the USBSerial, the last one under USBDevice example. Once the correct drivers are installed, I've compiled, loaded and ran the examples on a FDRM-KL25Z board and my coworker Fabio, did the same for his board LPC1768. The 2 COM ports appear ok on device manager in both computers. The COM port on the OpenSDA side works perfectly, (both machines). But the another one directly connected to the KL25Z128 / LPC1768, only receives data from the terminal, but not transmits. In other words, the function <<serial.scanf("%s", buf);>> really do it's job, but the <<serial.printf("recv: %s", buf);>> or the <<serial.printf("I am a virtual serial port\n");>>, do nothing at all. All mbed team, you should give a special attention in order to kill this bug. The purpose of the mbed project sounds really good and deserves it! We should not allow a bug like this to misrepresent this so complete library, on this so good initiative.