Section 1 of the Act says:
A person is guilty of an offence if—
(a) he causes a computer to perform any function with intent to secure
access to any program or data held in any computer;
(b) the access he intends to secure is unauthorised; and
(c) he knows at the time when he causes the computer to perform the
function that that is the case.
Under Section 3, (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
There is also the matter of "acquiring" the botnet, which will have involved
the payment of a sum of money to a criminal.