Hacking Primer

Hackers, crackers and Trojan horses:A primer
by PsychoGRWeb posted at: 10:59 a.m. EST (1559 GMT)
By David MandevilleSpecial to CNN Interactive & HACKOO!
(CNN) -- Two things terrify today's computer users: viruses and hackers. And just like viruses, most people don't understand hackers or what they do.
Hackers come in many varieties. The term "hacker" usually brings to mind three of these -- people who break the security of computer networks, people who break the security on application software, and people who create malicious programs like viruses. These aren't mutually exclusive, but it's a simple way to divide the activities that fall under "hacking."
Network hackers
These are the hackers you see in movies, usually as unattractive, introverted and anti-social -- or ultra-hip, sexy and connected. Real hackers don't fit those stereotypes. They aren't nerds living in darkened dorm rooms or multi-millionaire industrial spies. They are average people with strong computer skills and the desire to test those skills in ways that often prove illegal.
Network hackers engage in several sorts of activities. Some, like "denial of service attacks" or "mail bombs," are designed to swamp a computer network's ability to respond and perform its internal functions. For instance, a denial of service attack on a Web server floods it with bogus requests for pages. The server spends so much time trying to process these requests that it can't respond to legitimate requests and may crash. A mail bomb is similar but targets a victim's mail server. A number of businesses and Internet service providers have suffered these sorts of attacks in recent years.
No one connected to a computer network is really safe from hackers
Another form of network hacking involves penetrating a secure area by subverting its security measures. Network hackers might accomplish this by setting up programs that try millions of passwords until one is accepted. A hacker may set up "sniffers," programs that check data to find encrypted or sensitive information. Once they gather the information they can decode it, or if unencrypted, use it directly to find out more about a network and penetrate it more easily.
Once hackers get onto the machines that host networks, they can alter or remove files, steal information and erase the evidence of those activities. But many hackers break security systems just to see if they can do it. They may enter the system, look at the data within and never go back. For these hackers, it's more a test of skill than an attempt to steal or alter data.
Software crackers
Application software, such as programs for word processing or graphics, puts the power of a personal computer in the hands of a user, even one who doesn't know how the computer works. It's often expensive and, like anything else that's useful but expensive, there's bound to be someone who wants to get it free of charge. That's where "crackers" -- hackers who break software security -- come in.
These hackers develop their own software that can circumnavigate or falsify the security measures that keep the application from being replicated on a PC. For instance, you have a piece of software that requires a serial number to install. A software hacker does this in much the same way that network hackers attack network security. They may set up a serial number generator that tries millions of combinations of numbers and letters until it finds one that matches. The hacker could also attack the program at the assembly-code level, finding and altering the security measures.
One note: A software hacker is not necessarily a software pirate. A hacker may break the security and use the software, but a true pirate would also replicate and sell the cracked software.
Virus builders
Some hackers are also virus builders. Viruses, worms, Trojan horses and logic bombs are all forms of programs that can invade a system. Some are malicious, some aren't.
A virus is a program that may or may not attach itself to a file and replicate itself. It may or may not corrupt the data of the file it invades. It may or may not try to use all of the computer's processing resources in an attempt to crash the machine. If that seems vague, it's because viruses are tricky. They may be simple notes that say "Hello" -- or they may attack and corrupt the files at the core of the system, causing it to crash.
Worms invade a computer and steal its resources to replicate themselves. They use networks to spread themselves.
A Trojan horse appears to do one thing but does something else. The system may accept it as one thing, but upon execution it may release a virus, worm or logic bomb.
A logic bomb is an attack triggered by an event, like the computer clock reaching a certain date. It might release a virus or be a virus itself.
No defense
No one connected to a computer network is really safe from hackers. Luckily, most invasions or infections don't result in serious injury to the system that has been attacked.
The only real defense is limiting your risk by using virus scanners and enforcing security measures on network computers. But in the end, hackers see security systems as a challenge, not an obstacle.
For more information on hacking and security, take a look at these sites:
Technology and Society at the World Wide Web Consortium (W3C) -- The W3C tries to set and maintain standards for the portion of the Internet people are most familiar with, the World Wide Web. The Technology and Society domain seeks to influence public and private policy on issues, including security, arising out of the development of Web technology. The articles may be a little dry, but the information is good.
Electronic Freedom Foundation -- An organization dedicated to keeping the Internet an uninhibited medium for information, the EFF is an excellent source of information about security issues and legislation that affects the Internet.
David Mandeville is an application engineer at iXL.