What is a worm?

A computer worm is comparable to a computer virus, but unlike a virus a worm does not need to attach itself to an existing program. Instead, it is able to spread copies of itself from one computer to another without being activated by users.

Some worms have the ability to send themselves to everyone in your e-mail address book - and then to everyone in their e-mail address books, making the worms capable of spreading to millions of computers within hours. In the most extreme cases, worms have affected computer networks worldwide and drastically slowed down the Internet.

Worms typically exploit vulnerabilities in operating systems and spread through e-mail or other file transmission capabilities found on networked computers. They often hide in parts of operating systems that are automatic and usually invisible to you. It is common for worms to be noticed only when their uncontrolled replication consumes system resources, slowing or halting other tasks.

Many worms have been created only to spread and do not attempt to mess up computers they pass through. Other worms, however, carry a so-called "payload". A payload is code typically designed to do damage - it might delete files on your PC, encrypt files in an extortion attack, or attach itself to your outgoing e-mail. A very common payload for worms is to install a backdoor which can later be exploited by other malware, allowing the worm author to take control over infected computers.

The most famous and damaging worms - like MyDoom, Slammer, and Sasser - were all unleashed in 2003-2004 and since then major attacks have been rare. During 2007, the Storm Worm created a botnet containing millions of PCs. But in spite of its name, Storm Worm is in fact a Trojan horse with an executable file as an attachment.

Mobile devices have also experienced worm attacks. One example was Caribe which was able to send itself from one mobile phone to another across a network.

Description from BullGuard newsletter.

Access time Amount of time it takes for a hard drive to find and retrieve a piece of information. Also known as seek time.

ACPI advanced configuration and power interface. The latest standard that specifies how PC or laptop power can be efficiently managed. Features include activating devices only when required and reducing clock speed when full processing power is not needed.

ActiveX unlike Java, ActiveX is not a programming language, but a set of instructions on how an object should be used. ActiveX controls can be downloaded from the internet, and run just like Java applets. However, Java will only interact with your web browser, while ActiveX controls can access your Windows operating system.

ADSL asymmetric digital subscriber line. A permanently on, broadband connection to the internet using conventional phonelines. Data is downloaded to the PC faster than it is uploaded from the PC – hence the term ‘asymmetric’ is used to describe the connection.

AGP accelerated graphics port. An expansion slot linked directly to the motherboard’s system bus, enabling high-performance graphics. AGP graphics cards can access system memory directly, as well as using their own video memory. AGP 2X has a peak transfer rate of 512MBps (megabytes per second), while AGP 4X runs at 1.1GBps (gigabytes per second).

Ansi lumens Refers to the brightness of a projector. The higher this figure, the brighter the image will be. Anything in excess of 800 Ansi lumens should be viewable in daylight.

Anti-aliasing is a technique used to adjust jagged diagonal lines and curves in images caused by false frequencies (aliases) to make them look smoother. This process is commonly used to improve the appearance of fonts and pictures.

API application program interface. A common interface that allows programs to make use of services provided by the operating system or other applications. Winsock, for example, is an API that allows Windows and other programs to talk to TCP/IP for internet access.

Applet Program designed to be executed from within another program. Applets cannot be activated from an operating system.

Application Software program, such as a word processor, spreadsheet or game, that is designed for a specific purpose.

Ascii american standard code for information interchange. Ascii is the most common format for text files in computers and on the internet.

Atapi attachment packet interface. This is an extension to the EIDE interface specification that additionally supports CD-ROM and tape drives.

Athlon XP AMD’s processor, the Athlon XP, has a slower clock speed than its predecessors, but thanks to some clever tweaks of the architecture it is outperforming all the competition.

AVI audio video interleave. Designed by Microsoft to combine audio and video in a single track or frame to keep them synchronised. Files can be compressed using various audio and video coders (coder/decoder).

Computer Glossary B

Baseband The most common type of network. Data is transmitted digitally, each wire carrying one signal at a time.

Basic beginner’s all-purpose symbolic instruction code. A popular and simple programming language, which uses easy-to-understand statements. Microsoft’s Visual Basic provides a graphical interface for writing programs.

Bios basic input/output system. Software stored in ROM (read-only memory) and used to start a PC when it is switched on. It checks that all required hardware components such as memory, disk drives and keyboard are present, loads key parts of the operating system and tells it what hardware is available.

Bit The smallest unit of data, which has a value of 1 or 0 and is stored by a capacitor in a memory chip using different electrical currents. Abbreviated b in data transfer rates – for example, 50Kbps (50,000 bits per second).

Bluetooth Specification for linking devices such as mobile phones, computers and PDAs (personal digital assistants) over a short-range wireless connection. The maximum range over which it can operate is currently 10 metres, with data transfer rates of up to 721Kbps (kilobits per second) supported.

broadband Describes transmissions over a wire that can carry multiple signals at once. Cable TV uses broadband transmissions.

buffer underrun Recording data to CD-R is a real-time process and cannot be interrupted, so most drives come with a buffer of memory to store information to cover times when the PC is not supplying information. Buffer underrun occurs when this buffer is exhausted and the PC has not resumed sending information to the drive.

Bus The data path on the computer’s motherboard that interconnects the microprocessor and other components in expansion slots.

Bus Master An intelligent device such as a PCI adapter card that can gain control of the bus and use it to transfer data without involving the processor.

Bus Network A network configuration in which a single cable, laid out as one long branch, connects all the networked PCs.

Byte A group of eight bits used to represent a character or number with four bytes representing a word. The binary system is used, so a kilobyte is 1,024 bytes while a megabyte is 1,048,576 bytes (not 1,000,000 bytes). Abbreviated B in data transfer rates, for example, 30MBps (30,000,000 bytes per second).

Computer Glossary C

Cache Temporary storage area used to speed up different processes. A web browser keeps recently used web pages on hard disk cache, so it doesn’t have to download the same page again. A processor stores recent or frequently used instructions in chunks of very fast memory called level 1 and 2 caches.

CCD charge-coupled device. A CCD is used by digital cameras and scanners. It is a grid of light-sensitive cells that store an electrical charge proportional to the amount of light falling on them. The charge value in each cell is converted from analogue to digital and is used to build up a complete image.

CDMA code division multiple access. CDMA is a digital cellular technology. Unlike GSM, CDMA does not assign a specific frequency to each user. Instead, every channel uses the full available spectrum and the frequency is divided using codes.

Chipset A number of integrated circuits which carry out related tasks. This is the name often given to the core functionality of a motherboard, or to the chip that powers a graphics card.

client/server A network where all services and facilities such as email or file and printer sharing are provided to networked, or client PCs and controlled by separate, purpose-built systems called servers.

Cmos complementary metal oxide semiconductor. A process used to make chips, but in a PC is shorthand for a batterypowered chip on the motherboard, which stores basic system configurations and clock settings.

Compiler Special program that takes the instructions written in a programming language and turns them into machine code that a PC processor can understand.

Composite cable A video cable with yellow connectors on the end used to view digital cameras on a television.

Cookie A message sent by a web server to a browser and stored in a text file, usually called cookie.txt. The message is sent back to the browser every time a new request is made at the website. Cookies are mostly used to identify users and create site visit statistics on types of browser, operating systems and popular pages.

CPU central processing unit. A microprocessor chip that is the ‘brains’ of a computer. Its many functions include fetching and carrying out instructions for programs.

CRT cathode ray tube. A monitor technology that works by moving an electron beam back and forth across the back of the screen. Each time it passes across the screen it lights up red, green and blue phosphor dots on the inside of the screen to make up the images you see.

CMYK cyan, magenta, yellow, keystone black. These are the four basic colours used by inkjet and laser colour printers. A huge range of colours are created by a combination of overlaying and dithering.