Computer crime is defined as a criminal act that has been committed with a computer as the principle tool. These computer criminals are people with advanced knowledge of operating systems, phone systems, and other computer-related devices. Some computer criminals break into other people’s computers, and steal data, these criminals are known as hackers. Yet others might make a phone call without even paying for it, or receive phone services that they did not pay for, these people are known as phreakers. And yet there are other computer criminals that illegally copy software, these criminals are known as software pirates. Although authorities try to combat the doings of these criminals, computer crime is still a huge market for criminals of all kinds. They are able to gain access to computers using special tools, methods and programs. Some of these are back doors, viruses, and port scanners. The most popular form of virus is known as the Trojan horse, named after the Greek Trojan Horse.