NTL has used MAC addresses to track and register customers to the NTL internet service. As NTL had not supported the use of routers, or Xbox on the minority Set Top Box based Broadband Internet service, users had to use a clone MAC address feature to connect to the Internet when using an STB. This has become a common problem for people wishing to connect their Xbox to the existing internet connection through a router or PC connected to their STB, if they fail to use the official registration process. (These comments do not apply to the majority (>90%) use of cable modems).