AdWare - A software application in which advertising banners are displayed while the program is running; sometimes, also tracks user information, which makes it also spyware.

Anti-Virus Software - A class of program that searches your hard drive and floppy disks for any known or potential viruses.

Back Door - An means of access to a computer system that bypasses security mechanisms, installed sometimes by an authorized person, sometimes by an attacker.

Buffer Overflow - Type of attack that sends more data than a buffer was intended to hold; surplus data will overflow into adjacent buffers, corrupting or overwriting the valid data held in them or may. Data sent may include malicious code.

Browser HiJacker - Programming that alters your browser settings so that you are redirected to Web sites you had no intention of visiting.

Data Miner - In a malware context, a program that tracks and processes data about the user's browsing behavior for marketing purposes.

Denial Of Service (DOS) - An incident in which a user or organization is deprived of the services of a resource they would normally expect to have.

Directory Harvest Attack - An attempt to determine the valid e-mail addresses associated with an e-mail server so that they can be added to a spam database.

Distributed Denial-Of-Service Attack - One in which a multitude of compromised systems attack a single target, thereby causing denial of service for users of the targeted system.

E-mail Virus - Malicious computer code sent to you as an e-mail note attachment. The best two defenses against e-mail viruses for the individual user are (1) a policy of never opening an e-mail attachment (even from someone you know) unless you have been expecting the attachment and know what it contains, and (2) installing and using anti-virus software to scan any attachment before you open it.

Ethical Worm - Program used to automate network-based distribution of security patches.

Executable - Type of file containing a program that will start it to run; viruses are often sent in executable files that will run when the user opens the file.

Hybrid Virus - One that combines characteristics of more than one type of virus to infect both program files and system sectors. The virus may attack at either level and proceed to infect the other once it has established itself.

Hybrid Virus/Worm - Malicious code that combines characteristics of both those types of malware, typically featuring the virus' ability to alter program code with the worm's ability to reside in live memory and to propagate without any action on the part of the user.

IM Worm - Self-replicating malicious code that spreads in instant messaging networks.

In The Wild - Malicious computer code that spreads in the real world as a result of normal day-to-day operations.

Key Logger - A type of spyware program that records the user's keystrokes invisibly and either transmits them to the attacker on an ongoing basis or saves them to a secret file in the user's computer to be sent at a later time.

Klez - Worm that launches automatically when a user previews or reads an e-mail message containing Klez on a system that has not been patched for a vulnerability in Microsoft Internet Explorer mail clients.

Logic Bomb - Programming code designed to execute (or "explode") after some particular trigger event happens, such as a specific date.

Malware - Programming or files developed for the purpose of doing harm.

Macro Virus - Virus that infects a word processing application and causes a sequence of actions to be performed automatically when the application is started or something else triggers it. Macro viruses tend to be surprising but relatively harmless.

Nimda - Virus that caused traffic slowdowns as it rippled across the Internet, spreading through four different methods.

Password Cracker - A program used to identify an unknown or forgotten password, often used by a human cracker to obtain unauthorized access.

Patch - A quick-repair job for a piece of programming, often as a result of some discovered vulnerability.

Port Scan -Series of messages sent by someone attempting to break into a computer to learn which computer network services, each associated with a "well-known" port number, the computer provides.

Probe - An attempt to gain access to a computer and its files through a known or probable weak point in the computer system.

Spyware - Programming that is put in someone's computer to secretly gather information about the user and relay it to advertisers or other interested parties.

Stealth Virus - A virus that includes mechanisms that enable it to hide from anti-virus programs.

Trojan Horse - A virus in which malicious or harmful code is contained inside apparently harmless programming or data.

Virus - A piece of programming code usually disguised as something else that causes some unexpected and usually undesirable event. A virus is often designed so that it is automatically spread to other computer users. Generally, there are three main classes of viruses: file infectors, system or boot infectors, and macro viruses.

Virus Hoax - A false warning about a computer virus. Virus hoaxes are usually forwarded using distribution lists and will typically suggest that the recipient forward the note to other distribution lists. If you get a message about a new virus, you can check it out by going to one of several Web sites that keep up with viruses and virus hoaxes.

Worm - A self-replicating virus that does not alter files but resides in active memory and duplicates itself. Worms use parts of an operating system that are automatic and usually invisible to the user. It is common for worms to be noticed only when their uncontrolled replication consumes system resources, slowing or halting other tasks.

Zoo - A type of malware that exists only in virus and antivirus labs, not in the wild