Crime involving computer networks has always been in existence. However, the fact that the Internet is a public network which has been constructed from components whose structure and specification are publicly available has meant that the amount of computer-related crime has increased substantially since the mid-1980s. This crime ranges from nuisance activities such as sending unsolicited emails, known as spam, advertising services or products for sale, to chain letter scams which ask recipients of an email to send it on to a friend and deliver some money. There are also a number of crimes which are just electronic versions of existing ones: for example, Ponzi schemes, pyramid schemes, and share ramping. However, the Internet has made such crimes easier to carry out in terms of the number of potential victims and the speed of delivery of documents associated with the crime. The most serious crimes are perpetrated by crackers and involve intrusion into a private network. Since many of these networks have interfaces to the Internet it is now easier to enter them, although well-established techniques such as those involving the use of password sniffers and dumpster diving are still frequently used. Typical crimes include the salami attack in which very small amounts of money are taken from a financial account and added to the perpetrator's account, and the denial of service attack which ties up an important computer resource such as a processor and denies access to users of a network.