Computer Misuse Act 1990

Computer Misuse Act 1990
Computer Misuse Act 1990

United Kingdom Parliament
Long title An Act to make provision for securing computer material against unauthorised access or modification; and for connected purposes.
Statute book chapter 1990 (c. 18)
Introduced by Michael Colvin
Territorial extent England and Wales; Scotland; Northern Ireland
Royal Assent 29 June 1990
Commencement 29 August 1990
Other legislation
Amendments Criminal Justice and Public Order Act 1994, Criminal Justice (Terrorism and Conspiracy) Act 1998
Status: Amended
Text of statute as originally enacted
Official text of the statute as amended and in force today within the United Kingdom, from the UK Statute Law Database

The Computer Misuse Act 1990 is an Act of the UK Parliament, introduced partly in response to the decision in R v Gold & Schifreen (1988) 1 AC 1063 (see below). Critics of the bill complained that it was introduced hastily and was poorly thought out. Intention, they said, was often difficult to prove, and that the bill inadequately differentiated "joyriding" hackers like Gold and Schifreen from serious computer criminals. The Act has nonetheless become a model from which several other countries, including Canada and the Republic of Ireland, have drawn inspiration when subsequently drafting their own information security laws, as it is seen "as a robust and flexible piece of legislation in terms of dealing with cybercrime”[1].


R v Gold & Schifreen

Robert Schifreen and Stephen Gold, using conventional home computers and modems in late 1984 and early 1985, gained unauthorised access to British Telecom's Prestel interactive viewdata service. While at a trade show, Schifreen by doing what latterly became known as shoulder surfing, had observed the password of a Prestel engineer: the username was 22222222 and the password was 1234. This later gave rise to subsequent accusations that BT had not taken security seriously. Armed with this information, the pair explored the system, even gaining access to the personal message box of Prince Philip.

Prestel installed monitors on the suspect accounts and passed information thus obtained to the police. The pair were charged under section 1 of the Forgery and Counterfeiting Act 1981 with defrauding BT by manufacturing a "false instrument", namely the internal condition of BT's equipment after it had processed Gold's eavesdropped password. Tried at Southwark Crown Court, they were convicted on specimen charges (five against Schifreen, four against Gold) and fined, respectively, £750 and £600.

Although the fines imposed were modest, they elected to appeal to the Criminal Division of the Court of Appeal. Their counsel cited the lack of evidence showing the two had attempted to obtain material gain from their exploits, and claimed the Forgery and Counterfeiting Act had been misapplied to their conduct.

They were acquitted by the Lord Justice Lane, but the prosecution appealed to the House of Lords. In 1988, the Lords upheld the acquittal.[2] Lord David Brennan said:

We have accordingly come to the conclusion that the language of the Act was not intended to apply to the situation which was shown to exist in this case. The submissions at the close of the prosecution case should have succeeded. It is a conclusion which we reach without regret. The Procrustean attempt[3] to force these facts into the language of an Act not designed to fit them produced grave difficulties for both judge and jury which we would not wish to see repeated. The appellants' conduct amounted in essence, as already stated, to dishonestly gaining access to the relevant Prestel data bank by a trick. That is not a criminal offence. If it is thought desirable to make it so, that is a matter for the legislature rather than the courts.

The Law Lords' ruling led many legal scholars to believe that hacking was not unlawful as the law then stood. The English Law Commission (ELC) and its counterpart in Scotland both considered the matter. The Scottish Law Commission concluded that intrusion was adequately covered in Scotland under the common law related to deception, but the ELC believed a new law was necessary.

Since the case, both defendants have gone to write about IT matters extensively and, in the case of Gold, who detailed the entire case at some length in the Hacker's Handbook, actually presents at conferences alongside the arresting officers in the case.

The Computer Misuse Act

Based on the ELC's recommendations, a Private Member's Bill was introduced by Conservative MP Michael Colvin. The bill, supported by the government, came into effect in 1990. Sections 1-3 of the Act introduced three criminal offences:[4]

  1. unauthorised access to computer material, punishable by 6 months' imprisonment or a fine "not exceeding level 5 on the standard scale" (currently £5000);
  2. unauthorised access with intent to commit or facilitate commission of further offences, punishable by 6 months/maximum fine on summary conviction or 5 years/fine on indictment;
  3. unauthorised modification of computer material, subject to the same sentences as section 2 offences.

§§2–3 are intended to deter the more serious criminals from using a computer to assist in the commission of a criminal offence or from impairing or hindering access to data stored in a computer. The basic offence is to attempt or achieve access to a computer or the data it stores, by inducing a computer to perform any function with intent to secure access. Hackers who program their computers to search through password permutations are therefore liable, even though all their attempts to log on are rejected by the target computer. The only precondition to liability is that the hacker should be aware that the access attempted is unauthorised. Thus, using another person's username or identifier (ID) and password without proper authority to access data or a program, or to alter, delete, copy or move a program or data, or simply to output a program or data to a screen or printer, or to impersonate that other person using e-mail, online chat, web or other services, constitute the offence. Even if the initial access is authorised, subsequent exploration, if there is a hierarchy of privileges in the system, may lead to entry to parts of the system for which the requisite privileges are lacking and the offence will be committed. But looking over a user's shoulder or using sophisticated electronic equipment to monitor the electromagnetic radiation emitted by VDUs ("electronic eavesdropping") is outside the scope of this offence.

The §§2–3 offences are aggravated offences, requiring a specific intent to commit another offence (for these purposes, the other offences are to be arrestable, and so include all the major common law and statutory offences of fraud and dishonesty). So a hacker who obtains access to a system intending to transfer money or shares, intends to commit theft, or to obtain confidential information for blackmail or extortion. Thus, the §1 offence is committed as soon as the unauthorised access is attempted, and the §2 offence overtakes liability as soon as specific access is made for the criminal purpose. The §3 offence is specifically aimed at those who write and circulate a computer virus (see Simon Vallor) or worm, whether on a LAN or across networks. Similarly, using phishing techniques or a Trojan horse to obtain identity data or to acquire any other data from an unauthorised source, or modifying the operating system files or some aspect of the computer's functions to interfere with its operation or prevent access to any data, including the destruction of files, or deliberately generating code to cause a complete system malfunction, are all criminal "modifications". In 2004, John Thornley pleaded guilty to four offences under §3, having mounted an attack on a rival site, and introduced a Trojan horse to bring it down on several occasions, but it is recognized that the wording of the offence should be clarified to confirm that all forms of denial of service attack are included.[citation needed]

Latest situation

In 2004, the All-Party Internet Group published its review of the law and highlighted areas for development. Their recommendations led to the drafting of the Computer Misuse Act 1990 (Amendment) Bill which sought to amend the CMA to comply with the European Convention on Cyber Crime [3]. Under its terms, the maximum sentence of imprisonment for breaching the Act changed from six months to two years. It also sought to explicitly criminalise denial-of-service attacks and other crimes facilitated by denial-of-service. The Bill did not receive Royal Assent because Parliament was prorogued.

Sections 35 to 38 of the Police and Justice Act 2006 contains amendments to the Computer Misuse Act 1990.

Section 37 (Making, supplying or obtaining articles for use in computer misuse offences) inserts a new section 3A into the 1990 Act and has drawn considerable criticism from IT professionals, as many of their tools can be used by criminals in addition to their legitimate purposes, and thus fall under section 3A.

After the infamous News International phone hacking scandal in 2011, there are ongoing discussions about amending the law to define "smart" phones (i.e. those with Internet browsers and other connectivity features) as computers under the Act. This amendment may also introduce a new offence of (making information available with intent) i.e. publicly disclosing a password for someone's phone or computer so that others can access it illegally.[5]

The amendments

The amendments to the Computer Misuse Act 1990 by Part 5 of the Police and Justice Act 2006[6] are

Section 35. Unauthorised access to computer material[7]

Section 36. Unauthorised acts with intent to impair operation of computer, etc[8]

Section 37. Making, supplying or obtaining articles for use in computer misuse offences[9]

Section 38. Transitional and saving provision[10]

See also


  • Stefan Fafinski, Computer Misuse: Response, Regulation and the Law (Cullomption, Willan 2009)
  • Yaman Akdeniz, Section 3 of the Computer Misuse Act 1990: an Antidote for Computer Viruses! (1996) 3 Web JCLI [4] including reference to the case of Christopher Pile (aka 'the Black Baron') in November 1995.
  • Derek Wyatt, Computer Misuse Act (amendment) speech. [5]
  • The Law Lords' ruling
  • Data Protection Act 1998


  1. ^ IISS Global Perspectives – Power in Cyberspace. Q&A with Nigel Inkster, Director, Transnational Threats and Political Risk, IISS. 18 January 2011.
  2. ^ HL 21 April 1988, [1988] AC 1063 summary at [1]
  3. ^ Here Lord Brandon alludes to the classical myth of Procrustes, who would stretch his victims to fit a bed for which they were ill suited.
  4. ^ Computer Misuse Act 1990, s1 - s3
  5. ^ [2]
  6. ^ Police and Justice Act 2006
  7. ^ Police Act section 35
  8. ^ Police Act section 36
  9. ^ Police Act section 37
  10. ^ Police act section 38

External links

UK Legislation

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