Computer Misuse Act 1990. https://www.legislation.gov.uk/ukpga/1990/18/section/3

(1)A person is guilty of an offence if—

(a)he does any unauthorised act in relation to a computer;

(b)at the time when he does the act he knows that it is unauthorised; and

(c)either subsection (2) or subsection (3) below applies.

(2)This subsection applies if the person intends by doing the act—

(c)to impair the operation of any such program or the reliability of any such data;