Adware
A program that displays advertising material to computer users, potentially in a manner or context that is unexpected or unwanted.

Adware is sometimes considered a "gray" area in terms of ethics and legality. They range from legitimate programs that display unobtrusive content and are willingly installed by the user, all the way to programs that silently install themselves and barrage the user with inappropriate content.

Some adware will perform user behavior monitoring to determine the best advertising material to display based on the user's preferences; this function may or may not be disclosed to the user.

Backdoor
A remote administration utility which bypasses normal security mechanisms to secretly control a program, computer or network.

Backdoors are sometimes considered a form of riskware, as they can be legitimately used by trusted users or system administrators, but can also be misused by an attacker to remotely usurp control of the system.

Bluetooth-Worm
Bluetooth is a wireless communications technology, commonly used by computers and other electronic devices. A Bluetooth-worm primarily replicates by spreading over Bluetooth networks to infect other Bluetooth-enabled systems and devices.

Dialer
A program that connects the computer to the Internet via a telephone line and modem.

Malicious dialers secretly connect the computer to premium-rate lines, greatly increasing the usage charges payable by the user.

Email-Worm
A worm that mainly spreads via e-mail.

The worm may be delivered in an infected e-mail attachment, which usually requires the user to double-click and run the attachment before the worm can infect the system.

Alternatively, the worm may be delivered as code embedded in the e-mail message itself; in this case, the user may not need to do anything other than view the e-mail in order for the system to be infected, as the worm exploits a vulnerability in the operating system or web browser to automatically execute its code.

Exploit
A program or piece of code that is specifically written to take advantage of a vulnerability, in order to provide an attacker with access to a vulnerable computer system, program or network.

HackTool
A utility designed to access remote computers. Though legal, a hacktool can be used with malicious intent.

Hijacker
A program that hijacks a user's web browser or user session for its own purposes, usually to misdirect the user to another website, or to steal sensitive information.

Hoax
A program which does not function as claimed, and may have been promoted using deceptive or fraudulent means.

IM-Worm
A worm that spreads primarily on instant messaging networks, most commonly by sending messages with infected attachment to all of an infected user's contacts.
Intended
A program that contains bugs, or other problems, which prevent it from functioning as the author intended. It would have been malware, and future versions still might be, but the current version is defective.

IRC-Worm
Internet Relay Chat (IRC) is a form of real-time Internet chat and is designed for group communication in discussion forums known as channels. An IRC-worm spreads primarily over IRC channels, usually by sending a message with an infected attachment to all users who join a channel an infected user is already on.

Macro
Macros are mini-programs used in some applications to automate certain functions or instructions. Macros are commonly used to deliver, execute and hide malware, which are thus often referred to as "macro viruses".

Monitoring Tool
A program that can monitor and record all computer activities, including each keystroke typed on the keyboard.

Net-Worm
A worm that replicates over networks, most commonly through local area networks (LANs). Also known as a network worm, net-worms will create copies of itself on any accessible network shares (a hard drive or resource that can be accessed by any designated users of a network). Once on the network share, the worm can spread to other systems in the network.

P2P-Worm
A worm that spreads primarily over Peer-to-Peer (P2P) networks. Often, such worms will conceal themselves in temptingly named files, in order to lure a P2P user into downloading the file and executing the worm's file onto their own system.

Riskware
A program that is not malicious in nature, but may pose or introduce a security risk if improperly used.

Rogue
An antivirus or antispyware application that does not provide the functionality claimed, and may not work at all. Rogues are often promoted by deceptive or fraudulent means.

Rootkit
A technique or program used by malware to obscure the fact that a computer has been compromised. Rootkits work by directly interfering with the operating system and critical system mechanisms in order to disguise or "cloak" the malware's activities.

SMS-Worm
An SMS-Worm spreads by exploiting the Short Message Service (SMS) protocol used to send short text messages between mobile devices on the Global System for Mobile communications (GSM) network.

Spyware
A program that may compromise a user's personal or confidential information. Spyware is usually, but not always, installed on a system without a user's authorization or knowledge.

Spyware can vary widely in the kinds of actions they perform. Some common actions include displaying unsolicited pop-ups, hijacking a browser's home or search pages, redirecting browsing results and monitoring user activities.

Spyware is sometimes considered a "gray" area in terms of ethics and legality. Depending on the specific action, context of use and applicable laws, spyware could be considered legal and acceptable; dubious but unlegislated; or outright illegal and unethical.

Toolbar
A type of browser plug-in, toolbars are applications which are "added on" to Web browser programs to provide additional functionality. Many toolbars are innocuous, but some toolbars are designed to monitor a user's online browsing behavior.

Trackware
Software that monitors user behavior or gathers information about the user. The information gathered can sometimes including personally identifiable details, passwords or other confidential data.

Trojan
A program that appears to perform one action, while silently performing another action without the knowledge or authorization of the user.

A trojan typically does not replicate. There are numerous types of trojans, which are categorized based on the action(s) they perform.

Trojans were named after the Trojan Horse of Greek legend, and are sometimes referred to as Trojan Horse programs.

Trojan-Downloader
A trojan that downloads and installs programs on the targeted computer without the user's knowledge or authorization.

Trojan-Dropper
A trojan that contains other programs in its payload and installs them without the user's knowledge or authorization.

Trojan-Proxy
A trojan that forces the infected system to function as a proxy server in order to provide attackers with anonymous access to the Internet.

Trojan-PSW
A trojan that is capable of stealing passwords, account login and user details, and other confidential information from an infected machine. A more sophisticated trojan-PSW may also be capable of sending the stolen information to the attacker.

Trojan-Spy
A trojan that can function as, or install, a spy program such as a keylogger.


Virus

A program that replicates itself by infecting an executable file (referred to as a host) in such a way that the virus is replicated each time the host is executed.

A virus can be further categorized based on its technical features. A program does not need a destructive payload to be typed as a virus, but most viruses nowadays are designed to be harmful.

Vulnerability
A flaw or security loophole that may allow other users, applications or attackers to affect a program or system without the user's authorization or knowledge.

A vulnerability can be a flaw in a program's fundamental design, a bug in its code that allows improper usage of the program, or simply weak security practices that allow attackers to access the program without directly affecting its code.

Worm
A program that replicates by sending copies of itself from one infected system to other systems or devices accessible over a network.

Unlike viruses, worms can replicate independently; they do not need to infect a host in order to replicate.

There are many types of worms, which can be categorized based on the type of network they use to spread. For example, a Bluetooth-worm spreads mainly over Bluetooth networks, while IM-worms spread mostly over instant messaging networks, and so on. Some worms may also have multiple ways of spreading.

Worms used to more of a threat to network stability rather than system integrity, as replicating worms clogged up network connections and increased traffic load. Nowadays, many worms also include destructive payloads, making them much more threatening.