Ho, ho, ho: Bart Simpson joke featured on Melissa

Cracker - Crackers are hackers with attitude, ie the people the media usually blame for bringing down systems. They can be malicious, in it for the money, or merely mischievous. (see hacker)

Daemons - Not to be confused with the British internet service provider, a daemon is a programme which sits discreetly on a computer, usually doing useful things like logging people on to websites. In the recent Yahoo! case, however, daemons were set up to generate the bogus requests for information. Stands for disk and execution monitor.

Electrabel - This Belgian electricity company was attacked by a cracker threatening to shut off power supplies for two hours. Unimpressed by the company's argument that an interruption would cost lives, "Red Attack" proved their ability to carry out the threat by supplying Electrabel with a copy of the firm's computer code.

Hacker threatened a blackout: 'I have the power.'

Fallout - Despite prior warning Asia and the Middle East succumbed to the Chernobyl virus last year - on the 13th anniversary of the Soviet nuclear accident. Precious files were wiped and some computers were even robbed of the ability to turn themselves on.

Girlies - Hacking for Girlies are a group short on sugar and spice. They plastered the New York Times website with pornographic images. It was reportedly in retaliation against a book written about super-hacker Kevin Mitnick by a Times reporter. (see Kevin Mitnick)

Hacker - Confuse hackers with crackers and you risk offending all sorts of people. Hackers see themselves as noble artisans, studying computer systems and security and using their programming skill to expose loopholes. Intellectual stimulation rather than profit or malice is the motive, they say. Many turn legit and are employed to tighten software or systems.

Meltdown: Chernobyl virus hit on accident anniversary

Internet ethics - In response to the growth and severity of hacker attacks Deputy US Attorney General Eric Holder is calling for teenagers to be taught "internet ethics". "They know it's wrong to break into a person's house, yet they don't feel the same moral apprehension before breaking into a person's computer," he said.

John T Draper - A pioneer of phreaking. Known as Cap'n Crunch because he was famed for getting free long-distance calls from the American phone system by blowing a toy whistle which had come out of a box of cereal (Cap'n Crunch). Later went on to write the first word processing package for Apple.

Kevin Mitnick - A legend in hacker circles and across the internet community. Once heading the FBI's most wanted list, Mitnick has been accused of every cyber crime in the book. Just released following a five-year prison sentence, he is banned from using computers or even working for any employer with terminals in their buildings.

Kevin Mitnick: America's most wanted

Losing face - It is estimated that two-thirds of the companies who fall prey to hackers fail to report the crimes, fearing such admissions would scare away customers, particularly those nervous of e-commerce.

Maxus - This cracker is credited, as it were, with being responsible for one of the largest internet heists. Thousands of credit card details were reported last month to have been stolen from an online CD shop's database, and Maxus - reported to be a 19-year-old Russian - then told the shop he would publish the information unless he was paid $100,000.

Nato - During the Kosovo crisis, the military organisation's carefully managed propaganda war was rudely interrupted when the Nato website was "pinged" to its knees by hackers - reportedly based in the Serb capital, Belgrade. (see ping)

Orifice - Back Orifice and Back Orifice 2000, are the charmingly named inventions of hackers' group The Cult of the Dead Cow. Designed to show embarrassing flaws in Microsoft products, once installed the program allows a hacker to remotely control your PC.

Bill Gates: Microsoft is a prime hacking target

Ping - This involves sending a simple message to another computer, and it "pinging" back to you. Used as a means of testing that two machines can communicate, malicious pings like those to the Nato site cause network meltdown.

Quack! - Denial of service attacks, the technical name for the virtual traffic jams of useless data inflicted on Yahoo!, Amazon, CNN, eBay and others this week, make companies into sitting ducks. With IT departments snowed under, crackers can fillet the disrupted network for confidential information.

Routers - Computers which tell all those ones and zeros in cyberspace where they are, and how to get where they have been told to go. The Yahoo! crack used zombie computers to fool routers into sending the bogus information to the sites.

Hackers and crackers can seriously disrupt e-commerce

Smurf - These programs can be used to bombard sites with requests - it makes it possible for the requests to look like they have come from another address and making those requests multiply and blossom into a huge amount of information.

Tracks - By switching between computers and carefully erasing any identifying marks, the crackers were probably able to cover their tracks. But they can be sure that the FBI investigation will be getting out its biggest magnifying glass to look for clues.

United Loan Gunmen - Though woefully deficient in the grammar stakes, this hackers' group recently hit the website of American TV network ABC, replacing the front page with a poorly worded tirade against "old media".

Virus - Strains like the infamous Melissa can of course do horrible things. Or harmless things, depending on how mean the person who wrote the virus is. Where they actually come from is a subject for debate, particularly in internet chat rooms. Conspiracy theorists exonerate spotty teenage stay-at-homes, blaming instead various governments and even the canny software makers themselves.

Wobbler - Don't believe all you read. Feeding off a mix of millennial angst and residual technophobia, Wobbler is just one of numerous virus hoaxes circulating by e-mail. Countless useful hours can be lost attempting to guard your PC from "e-flu", "Irina" and the "Hitler" virus - none of which exist.

X-Force - Hackers don't get things all their own way. US firm Internet Security Systems claim their X-Force team of programmers decoded Back Orifice 2000 in under a day.

Yahoo! - Despite its mighty servers, the popular service was reportedly drowned by up to one gigabyte a second of incoming data in the recent denial of service attack. That's more information than most sites would receive in a year.

Zombies - the computers which attacked Yahoo!'s and the others are thought to be zombies, owned by third parties but taken over by the crackers to send the huge amount of information to the sites. Not to be confused with zombie websites, which have passed their useful life but are maintained as if in aspic.