Trojan horses:

A Trojan horse is a malware, that performs a malicious action, but has no replication abilities. Coined from Greek mythology's Trojan horse, a Trojan may arrive as a seemingly harmless file or application, but actually has some hidden malicious intent within its code. Trojan malware usually have a payload. When a Trojan is executed, you may experience unwanted system problems in operation, and sometimes loss of valuable data.

Spyware:

Spyware is a broad category of malicious software designed to intercept or take partial control of a computer's operation without the informed consent of that machine's owner or legitimate user. While the term taken literally suggests software that surreptitiously monitors the user, it has come to refer more broadly to software that subverts the computer's operation for the benefit of a third party. Malicious websites may attempt to install spyware on readers' computers. Spamblog triggers a pop-up that offers spyware in the guise of a security upgrade.

Adware:

Adware is ads-supported software that displays pop-up advertisements. Adware is usually available via free downloads from the Internet. Adware is often bundled with or embedded within freeware, utilitarian programs like file sharing applications, search utilities, information-providing programs (such as clocks, messengers, alerts, weather, and so on), and software such as screen savers, cartoon cursors, backgrounds, sounds, etc. Although seemingly harmless, some adware programs may track your Web surfing habits. Deleting adware may result in the deletion of the bundled freeware application.

Scams and shams:

Scams and shams include email messages that promise material gain or even luck to recipients who forward them to others users. Some luck-based hoaxes, often called chain letters, play on people's fear of bad luck. Money-based hoaxes offer incredibly quick cash for simply forwarding a message. Certain popular scams have tricked users into investing their own money in fruitless investments.

Malware:

A malware is a program that performs unexpected or unauthorized, but always malicious, actions. It is a general term used to refer to viruses, Trojans, and worms. Malware, depending on their type, may or may not include replicating and non-replicating malicious code. Due to the many facets of malicious code or a malicious program, referring to it as malware helps to avoid confusion. For example, a virus that also has Trojan-like capabilities may be called

Worms:

Worm is a self-contained program (or set of programs) that is able to spread functional copies of itself or its segments to other computer systems. The propagation usually takes place via network connections or email attachments. worm is similar to a virus in that it makes copies of itself, but it does not need to attach itself to a host (another computer program) in order to survive. Instead, when executed, it can simply replicate itself from machine to machine via a network. Like viruses, however, a worm can perform secondary actions ranging from merely nuisance level to highly destructive.

Greyware:

Greyware is a malicious software or code, that is considered to fall in the "grey area" between normal software and a virus. Greyware is a term for which all other malicious or annoying software such as adware, spyware, trackware, and other malicious code and malicious shareware fall under.

Hoax:

A hoax is an attempt to trick an audience into believing that something false is real. Generally there is some material object involved, which is actually a forgery. Unlike a fraud or con (which usually has an audience of one or a few), which are made for illicit financial or material gain, a hoax is often perpetrated as a practical joke, to cause embarrassment, for personal aggrandizement or to provoke social change through awareness. Many hoaxes are motivated by a desire to satirize or educate by exposing the credulity of the public and the media or the absurdity of the target.