The idea is that you would use a second factor like a text message to authenticate your phone either permanently or for something like 30 days . If someone steals your phone , as someone said above , you have the phone PIN as a second authentication method . If someone tries using another device with your stolen credentials as in the OP ' s example they won ' t have your phone to get the texted code . There are also offline twofactor authentication methods like Google Authenticator . <| sep |> tldr How can I become a controlling parent ? Chill out . Your mind will change when you have kids . They will surprise you . <| sep |> Guess this can finally settle that 2448 is Professional Cat Thruster . <| sep |> 1 . Quake Live 2 . Quake 43 . Unreal Tournament 994 . Quake 35 . Warsow 6 . Unreal Tournament 20047 . Doombringer 8 . Reflex 9 . Half Life 10 . Quake World