1.Hoax - An email that usually states that it is harming the computer, but does not actually do what it says. Some hoaxes ask the reader of the email to perform a damaging process, such as deleting an important file. Most hoaxes are spread by people who do not know that the email is a hoax and who are hoping to alert others to a potential virus.
2.A Trojan horse: Trojan-his in computing is a generally non-self-replicating type of malware program containing malicious code that, when executed, carries out actions determined by the nature of the Trojan, typically causing loss or theft of data, and possible system harm. A Trojan often acts as a backdoor, contacting a controller which can then have unauthorized access to the affected computer.
3.Worms: A program or algorithm that replicates itself over a computer network and usually performs malicious actions, such as using up the computer's resources and possibly shutting the system down.