This Practice Note explains the offences that can be committed under the Computer Misuse Act 1990 (CMA 1990). These include the offence of causing a computer to give unauthorised access to data or programmes (computer hacking), the offence of unauthorised access with intent to commit further offences and the offence of committing unauthorised acts with intent to impair the operation of a computer. It also explains the offence of unauthorised acts committed in relation to a computer which cause or create a risk of serious damage of a material kind introduced by the Serious Crime Act 2015. This note also covers the offence of making, supplying or obtaining articles for use in offences under the CMA 1990, ss 1, 2, 3, 3A or 3ZA, as well as the elements of all offences and the sentences which may be imposed on conviction. The territorial extent of the computer hacking and computer misuse offences are also explained.