In summary, the universal Turing machine uses a non-binary alphabet but is only meant to simulate Turing machines with a binary alphabet given a description of

In summary, the universal Turing machine uses a non-binary alphabet but is only meant to simulate Turing machines with a binary alphabet given a description of the Turing machine in a defined format and its input. By making the initial tape content of the simulated Turing machine non-binary, the universal Turing machine can be made to execute a further Turing machine contained in the input of the simulated Turing machine. Whether this works also depends on the description of the simulated Turing machine but the authors claim that most machine descriptions are exploitable but without any further discussion of this. A possible fix would probably be to simply halt when the Universal Turing machine encounters something other than zero or one in the region of the tape that represents the tape of the simulated Turing machine except for the symbol indicting the head of the simulated Turing machine.