The unknown user name or passwords can be learnt easily. The only way is reset your modem for the factory settings. There is a hidden reset button on every kind of modem devices. When your device working, by using a needle or a toothpick by holding on the button for 20 seconds turns back your device to factory settings. In this process, it is normal to break your internet connection because your existing Internet settings to be reset. Note: If you have not enough information, it is obviously recommended that you should get help from a person who has that kind of knowledge.