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Glossary of Virus-Related Terms
Dave Carlson - January 20, 1990

These terms are not all-inclusive, nor are the definitions very technical. This list defines terms you may encounter when you read articles and information about computer viruses.

Gain entry to a system or program through some electronic means. Access to disks has two names: Read Access (look at data on a disk) and Write Access (change or add data to the disk).
The process a computer virus uses to turn itself on and perform some function. Often a virus will activate on a pre-determined date or event.
Addressable Sector
A section of a disk that the computer’s operating system can identify and find.
ANSI (American National Standards Institute)
An organization that develops computer standards in the United States. ANSI.SYS is a system file that controls computer video activity.
Applications Software
Programs that do some useful function and produce some type of output (e.g., word processing or graphics).
Archive Bit
A code bit that the operating system uses to identify if a file has been backed up.
ASCII (American Standard Code for Information Interchange)
A seven-bit code established by ANSI (see ANSI). It is used to maintain compatibility between digital devices (See EBCDIC).
The file your computer runs when it first loads a disk (hard disk or floppy diskette). It contains the commands you want your computer to execute first.
Back Door
A secret bypass of a computer system’s security procedures. Back doors often are placed in a program or system by a well-meaning programmer during initial testing. These back doors usually are eliminated before final product release, but sometimes they are overlooked (accidently or intentionally). (Also may be called Trap Door.)
Back Up
Making an extra copy of programs and data to use to restore a system if something happens to the original data on a disk. This is one of the best ways to protect programs and data from virus destruction. CAUTION: Even backups may be infected by a virus. If you suspect a virus may be in your backup files, clean them with appropriate software or don’t use them.
Basic Input-Output System (BIOS)
BBS (Bulletin Board System)
Automated computer communication system which can be controlled from a remote location. Usually capable of sending messages between computers through a modem. People access and post notes on the bulletin board information systems available (CompuServe, Source, etc.).
Base 2 number system. Consists of the digits 0 and 1. Used by computers to identify off and on states and represent data.
BIOS (Basic Input-Output System)
A read-only set of commands built into a computer that controls input and output operations.
Bit (Binary Digit)
A single piece of digital information used by a computer to identify data. Represented by 1 or 0 in computer machine language. (See Binary.)
A program written to search for and fill all unused computer memory. It runs until the computer operating system can find no more room for programs or data.
This means to “start” the computer. A cold reboot means that the power is turned off and then back on (using the power switch or reset button). A warm reboot means that the system is reset using software or by pressing Ctrl-Alt-Del.
Boot Sector
This is the portion of a disk where the operating system stores system configuration information. The computer uses this information to prepare itself for normal operations.
Boot Sequence
The steps a computer takes to prepare itself for operation when it is turned on or reset.
Boot Track
That portion of the disk (usually Track 0) where the operating system stores system configuration information. The computer uses this information to prepare itself for normal operations. It is like a table of contents for the disk. Also called Boot Sector. The boot track/sector often is the target of computer virus attack.
Bootable Disk
A disk that has been prepared with the operating system to contain certain programs and files needed to start computer operations.
Location in computer memory reserved for temporary storage of data until needed for some computer operation or moved to permanent storage.
Bulletin Board
Electronic mail box used to store and retrieve computer messages. Usually accessed with a modem or some other telecommunications device.
Something in the program code (usually a programming error or oversight) that makes a computer do other than what the program author wanted it to do. The term originated with a real insect. An early computer malfunctioned when a moth got stuck in one of the electronic relays inside the computer. Many viruses contain bugs that make the program even more dangerous than its author intended.
Combination of eight bits that represent a binary character to a computer. (See Bit.)
A message (usually left on a computer bulletin board) asking for help solving a problem by running a certain program.
A number calculated based on the contents of a computer file. Many different methods are used to calculate a checksum. If a program is altered by a virus (or something else), the file checksum will change. Many anti-virus programs use the checksum calculation to scan for possible virus activity.
CMOS (Complementary Metal Oxide Semi-Conductor)
Low-power computer chip (semi-conductor) used for ROM/RAM in AT type computers. Location for permanent storage of setup and configuration information. Usually configurable by user through a special setup program. Records data such as: date, time, memory size, type of disk drives, etc. A virus that changes the contents of CMOS may be difficult to stop, because many times this type of memory needs special equipment to access.
The characters and symbols of a program that tell a computer what to do. It is written in some type of computer language.
The main disk operating system (DOS) program that contains most of the commands to make the computer operate. It loads part of itself to function as Terminate-and-Stay-Resident (TSR) commands. It works with two hidden system files to help configure and run the computer.
Computer Vaccine
Software or hardware designed to protect a computer from a virus infestation.
Computer Virus
A piece of malicious programming code (usually small) designed to replicate itself within an operating environment, take over system resources, and alter or destroy programs or data files. (NOTE: The plural of virus is viruses.)
The first system file a computer automatically executes. This file tells your computer how it should configure itself for operation each time it is turned on.
Control Character
Special character recognized in a computer to perform a special function. Based on software design – usually sent to the computer by processing a specific key (often the Ctrl or Alt key).
Special computer chip designed to perform a specific function, such as performing calculations to support number-intensive operations (e.g. spreadsheets, computer aided design, etc.). It relieves some of the work normally performed by a CPU. (See CPU.)
Core Wars
A computer game developed in the 1960s. Two programmers would pit their skills against each other to see who’s program could take control of the memory core of a computer. The winning program was the one which occupied the most memory area when the game ended. Sometimes also called Code Wars. (See Redcode.)
CPU (Central Processing Unit)
The computer brain chip. Controls the flow of data and operations of the computer. Performs all computer calculations (unless the computer has a co-processor installed). (See Co-Processor.)
Someone who is obsessed with breaking into a software or computer security system. These people often have an inflated ego and may leave messages to let others know they have succeeded.
When a computer system stops working or locks up, so the operator needs to reboot to get things going.
A name for hackers who try to create or defeat virus programs. They are a group of highly-skilled programmers who attack each other’s systems to see if they can defeat each other’s defense (while maintaining a defense of their own).
Often called hacker heaven, it is the theoretical space where cyberpunks play their games.
Digital characters received, used, transmitted, and stored by a computer.
Data Diddling
Fooling around with data files and programs just to see what they do. It often is a harmless, yet annoying, pastime of hackers.
A sort of table of contents for a disk. It contains the name, size, and creation date for each file on the disk. A Root Directory is the first level of a multi-level directory system. A Sub-Directory is a subordinate directory to a root directory. Directory structure is called a Tree (like a family tree).
Can refer to both hard disk and floppy diskette.
Distributed Virus
A computer virus that is divided into separate sections (sub-programs). A typical distributed virus will have a main control module (usually placed in a disk’s boot sector) that controls the actions of each sub-module. These are the most dangerous types of viruses, coded by highly-skilled programmers. These are very intelligent viruses that can do almost anything imaginable inside a computer system.
DOS (Disk Operating System)
The collection of programs and files the computer uses to perform disk and housekeeping operations (like displaying screen prompts and running programs).
When a computer system is not working for any reason. (See Up.)
Usually refers to activity on a BBS. Copying a program or file from another computer – transferring from “up there” to “down here.” (See Upload.)
EBCDIC (Extended Binary Coded Decimal Interchange Code)
An eight-bit code established by International Business Machines (IBM). Usually used to transfer data between mainframe and mini-computers. (See ASCII.)
Data that has been coded or cyphered. It can be read only by those using an appropriate key phrase or symbol.
Executable Code
The programs a computer uses. These files normally have an extension of: .BAT, .COM, .EXE, or .SYS (and others).
An addition to a file name. Some extensions tell DOS the program can be executed (e.g., .COM and .EXE). Other extensions can be used to identify the type of data stored in the file (e.g., .DOC and .WK1).
FAT (File Allocation Table)
A place on a disk where the computer stores information about what is on the disk (like a table of contents or index). It identifies file name, location, size, and other information the computer needs to use the file.
A collection of related data and information that the computer identifies by a unique name. Files can contain programs or data. Unless specifically defined, it usually means anything (other than a directory) that is displayed as a name by the DOS DIR command.
File Allocation Table (FAT)
A place on a disk where the computer stores information about what is on the disk (like a table of contents or index). It identifies file name, location, size, and other information the computer needs to use the file.
Computer instructions usually stored in a computer chip. It is used by the computer and operator, but the operator cannot change it without special equipment. An example is BIOS. (See BIOS.)
Flying Dutchman
A feature of many Trojan programs. After doing its dirty work, the program will erase all traces of itself from memory and disks to defeat further investigation.
Programs and files distributed without charge. Sometimes referred to as Public Domain Software, but the author may retain ownership. If the author requests a fee or registration, it is called Shareware.
GIGO (Garbage In – Garbage Out)
A computer will do exactly what a programmer tells it to do, even if the action was not the programmer’s intent. (See Bug.)
A problem with a computer’s operation. It can be caused by a variety of things (i.e.: Program bug, power failure, and conflicting programs).
Hacked Program (Sometimes called Pirated Programs.)
A program (usually a normal commercial program) which has had its copy-protection system broken or modified by a hacker or cracker. There have been reports of hacked programs containing viruses to punish those who illegally use them.
A person who likes to fiddle with computers and computer files. Often, the hacker will attempt to break into other computer systems. Hackers are not always malicious, but always are curious.
Hard Drive
A rigid magnetic disk storage device permanently sealed in an electronic container. Stores large amounts of data. Also called a fixed disk.
The parts of a computer or system you can touch and see. It is what allows the software to perform some task. It is something you can beat on if you need to vent your frustrations on the computer. (See Software.)
Hidden File
A file that is on a disk and can be executed or accessed by the system, but does not show up in the disk directory when files are listed by the operating system (e.g. DOS DIR command).
Something everyone needs once in a while from a significant other. (Especially when you can’t release your frustration on the computer hardware.)
IC (Integrated Circuit)
Computer chip used to store data or perform some type of computer operation. Usually composed of the equivalent of millions of transistors and other electronic components.
KB (Kilobyte)
A thousand bytes.
LAN (Local Area Network)
Computers or other telecommunications equipment linked into networks by wires or electronic devices. Many computers and peripherals can be connected. Usually restricted to a small geographic area – often in a single building or close group of buildings. (See WAN.)
Logic Bomb
A program or segment of code which triggers an unauthorized, malicious act when some predefined condition exists (i.e.: it may delete all hard drive files on a particular date).
Something left out of software or hardware which lets someone get around a computer security control process.
Mail Bomb
A logic bomb or virus that is placed into an electronic mailing system.
MB (Megabyte)
A million bytes.
Modem (MOdulator / DEModulator)
Electronic device that modulates (codes for a communication carrier) a signal to transmit data, then demodulates (decodes) that signal received by a computer. Usually used to send data between computers using a telephone line.
Microsoft - Disk Operating System (See DOS.)
Object Code
The actual machine language code that a computer can run. It can come from several language sources and usually contains routines from the language library module. It normally cannot be read by people. (See Source Code.)
Operating System
See DOS.
Hardware device which can be attached to a computer system to expand its capabilities (includes: monitor, keyboard, mouse, printer, scanner, etc.).
Phone Phreak
Someone who is obsessed with using a computer to communicate with other computers using a telephone system, frequently to avoid long distance charges.
A formal set of rules, established by some recognized agency. Defines format, timing, and other parameters for transmitting data between two or more computing devices.
RAM (Random Access Memory)
That portion of a computer’s memory which is available for the operating system and user. It is where user programs are loaded from disk.
Random Access Memory (RAM)
That portion of a computer’s memory which is available for the operating system and user. It is where user programs are loaded from disk.
Read-Only Memory (ROM)
That portion of a computer’s memory which is reserved for the computer’s use. An operator can read and use the information in ROM, but cannot store any data there.
To restart the computer from the beginning. (See Boot.)
The code used in the game Core Wars. It follows established design rules. (See Core Wars.)
The process of virus reproduction. Either copying itself or attaching to another program.
ROM (Read-Only Memory)
That portion of a computer’s memory which is reserved for the computer’s use. An operator can read and use the information in ROM, but cannot store any data there.
Salami Slicer
A program that operates in the background to steal program time form another application (usually on a mainframe computer).
A addressable section on a disk that stores data.
Software distributed on a try-before-you-buy basis. It is software owned by the author who retains the copyright. If you like the software and decide to use it, you are morally bound to send the author the requested registration fee. It is legal to copy and distribute this software (the “unregistered” version) for other computer users to try. You can’t collect payment for the program, but you can change a nominal fee for the copy and mailing service (usually less than $10).
The programs and files used by a computer. A user is able to change it with a computer. (See Firmware.)
Source Code
Computer program code that people can read. It must be assembled or compiled (put together and translated into computer machine language) into code for the computer to run. (See Object Code.)
The deliberate act of getting another person or system to take a wrong action. (i.e.: A program that looks like an entry screen can capture a password and transmit to its nefarious owner.)
A utility program (i.e.: an editor or compiler) that makes a back-up copy of working programs – usually under a different name for recovery later by its unscrupulous user.
System Files
The files an operating system uses to control and manage a computer. (See DOS.)
Tape Worm
Program that travels through a system gobbling up files. (See Worm.)
Terminate-and-Stay-Resident (TSR) Program
A program that loads itself into computer memory and stays there to work in the background. Several programs are available with this option. They are ready to spring into action with the touch of a pre-defined hot-key. (Same thing as RAM-Resident program.)
A program that operates in the background to capture passwords or other information.
Time Bomb
A program designed to activate at a pre-determined time or date. Many virus programs contain time bomb segments.
Trap Door
A secret bypass of a computer system’s security procedures. They often are placed in a system by a well-meaning programmer during initial testing. They usually are eliminated before final product development, but sometimes they are overlooked (accidentally or intentionally). (See Back Door.)
Trojan Horse
A program that looks normal, but contains some kind of harmful code. This is the most commonly used method for computer-based fraud. It is often used as a vehicle to transmit a virus into a system.
NOTE: Trojan Horse comes from a hollow wooden horse given to the city of Troy as a gift from the Greeks. (Greek legend told by Homer in the Iliad and Odyssey.)
When a computer system is working as expected. (See Down.)
Copying a program or file to another computer – transferring to “up there” from “down here.” Usually refers to activity on a BBS. (See Download.)
See Computer Vaccine.
See Computer Virus.
WAN (Wide Area Network)
Same idea as a LAN. However, parts of the WAN are great distances from each other – like in different cities or even across oceans. Can use telephone lines, microwave relays, or satellite stations. Can link several LANs to each other. More difficult to secure than a LAN. (See LAN.)
A derogatory term used by Ross Greenberg to describe the “slimeballs” who release computer viruses into the world.
Worm Program
A self-contained program that destroys data, but does not reproduce itself like a virus (however, a virus can contain worm code). Worms originally were developed to tap unused network resources for running very large or complex computer programs. Most worm programs have been modified to eat memory or program code. Some computer historians attribute the creation of this term to Joanne Dow. (See Tape Worm.)
Write Protect
To physically (i.e. write-protect tab) or electronically turn off a drive’s ability to write data to a disk or recordable media. When you put a write-protect tab on a floppy disk, the tab blocks a signal of light in the floppy drive. When this light is blocked, the drive write mechanism is turned off.

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