Why does my mobile phone send a text message to an unknown number after midnight?

If it's a fake phone, you can be sure it's an advertising rogue program that comes with the mobile phone. It will send instructions to the server, deduct your phone bill and make huge profits. If it is a smart phone, it is infected with a virus, which can be detected by scanning with security guards. If it is parallel imports, it may be that the firmware package tampered with the machine and installed a virus, which can only be removed by refreshing the machine.