Microsoft's Xbox Live gaming service contains automated security checks which ban users suspected of modchip use. At logon time, Xbox Live conducts a check of the currently running BIOS. If it differs in any way from the original BIOS, that particular Xbox (which is uniquely identified by a code in the motherboard's onboard ROM) is banned from the service. Some modchips include a manual switch which can be attached to the exterior of the case and used to switch the modchip on and off. When switched off, the Xbox will boot the original BIOS and dashboard, and allow the use of Xbox Live with an original game as if no modchip were present at all. As seen in the popular Xbox Live game, Halo 2, Modders still find ways to get around the mod bans implemented by Microsoft and compete actively against players with unmodded, legitimate consoles.
Finally, Xbox Live also maintains a database of the hard drive serial numbers associated with each particular Xbox (commonly referred to as the 'Marriage Theory'). If the user has replaced the original Xbox hard drive with a larger one, they may become banned from the service even if their modchip is disabled. This pairing of serial numbers is created at the user's first login, so if the new hard drive is locked with the original hard drive's key using a specialized dashboard like Evolution-X, it is possible to use a non-original hard drive on Xbox Live, as long as the Xbox never logged on to Live with its original drive.