"(1) A person is guilty of an offence if— (a) he does any act which causes an unauthorised modification of the contents of any computer; and (b) at the time when he does the act he has the requisite intent and the requisite knowledge. (2) For the purposes of subsection (1)(b) above the requisite intent is an intent to cause a modification of the contents of any computer and by so doing— (a) to impair the operation of any computer; (b) to prevent or hinder access to any program or data held in any computer; or (c) to impair the operation of any such program or the reliability of any such data. (3) The intent need not be directed at— (a) any particular computer; (b) any particular program or data or a program or data of any particular kind; or (c) any particular modification or a modification of any particular kind. (4) For the purposes of subsection (1)(b) above the requisite knowledge is knowledge that any modification he intends to cause is unauthorised. (5) It is immaterial for the purposes of this section whether an unauthorised modification or any intended effect of it of a kind mentioned in subsection (2) above is, or is intended to be, permanent or merely temporary."
"(7) A modification of the contents of any computer takes place if, by the operation of any function of the computer concerned or any other computer— (a) any program or data held in the computer concerned is altered or erased; or (b) any program or data is added to its contents; and any act which contributes towards causing such a modification shall be regarded as causing it. (8) Such a modification is unauthorised if— (a) the person whose act causes it is not himself entitled to determine whether the modification should be made; and (b) he does not have consent to the modification from any person who is so entitled."
"But if an individual, by misusing or bypassing any relevant password, places in the files of the computer a bogus e-mail by pretending that the password holder is the author when he is not, then such an addition to such data is plainly unauthorised, as defined in section 17(8); intent to modify the contents of the computer as defined in section 3(2) is self-evident and, by so doing, the reliability of the data in the computer is impaired within the meaning of section 3(2)(c)."