Not all acts of hacking will amount to terrorism. Under the Act, the use or threat of an action “designed seriously to interfere with or seriously to disrupt an electronic system” will be a terrorist action only if it is both –
Designed to influence the government or to intimidate the public or a section of the public, and
Made for the purpose of advancing a political, religious or ideological cause.
The definition is wide enough to cover "traditional" hacking where data on a system is corrupted and also denial of service attacks which have become an increasing problem in recent years. These are attacks by individuals who flood a web server with false and untraceable requests for information, overwhelming the system and ultimately crashing it.
However, the Act does not introduce a new offence of terrorism and does not lay down any penalties for such hacking actions. The Act does give additional powers to the police in dealing with terrorist acts, but hackers would still be prosecuted under existing laws.
The main anti-hacking laws of the UK are contained in the Computer Misuse Act 1990, but the wording of that Act is such that it could be difficult to use it to prosecute someone for a denial of service attack. Instead, in England, a denial of service attack might be prosecuted under the Criminal Damage Act; in Scotland, such an attack could be prosecuted as malicious mischief.
Penalties are provided for being connected with a proscribed organisation. The Act lists these and others can be added by the Secretary of State.
Membership or support of such an organisation can lead to a sentence of up to 10 years in prison and/or a fine. Even wearing an item of clothing or carrying an article relating indicating allegiance to such an organisation can lead to six months in jail.
The full text of the Act can be found at
http://www.legislation.hmso.gov.uk/acts/acts2000/20000011.htm.