The advance of information technology and computer technology has led to a corresponding increase in computer crime. There is no accepted definition of computer crime. Computers may be the subject of a crime, such as theft, or a computer may be used to commit a crime. Typically a computer is used, or misused, to elicit or manipulate data or processing. Simple unlawful access to a computer system can be regarded as an offence. Telecommunications may be involved. The result may be a transfer of funds or of confidential information. Sending an email to place a virus can be unlawful. The free flow of information has generated undesirable and abhorrent material. The public has expressed concern about pornography, information on how to make bombs and information about suicide techniques. New offences have been created in response to these concerns. Persons gaining unlawful access to computers for these purposes are typically referred to as crackers: hackers with malicious intent. Many crimes that are not specifically related to computers can be substantially facilitated by the use of computers. Crimes involving electronic commerce typically involve the use of computers and telecommunications. This area is often referred to as cybercrime.

In surveys undertaking by the Australian Computer Emergency Response Team (AusCERT), the most common breaches involved viruses (programs or codes that can replicate themselves and infect computers without the owner's consent and often without the owner's knowledge), worms (programs or codes which replicate themselves using a network system, and that are designed to cause malicious damage) and Trojan infections (code incorporated into an existing program which gives the appearance of performing a desirable function but which performs malicious functions).