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 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 was recognised that the wording of the offence needed to be clarified to confirm that all forms of denial of service attack are included.