Malware (short for MALicious SoftWARE) is a prominent threat in our increasingly connected world. In short, malware is any program created with the purpose of causing damage to a computer system or compromising the security of a computer system. Pretty much all the "internet nasties" you've heard of fall into the broad category of malware. These include viruses, worms, Trojans, keylogger, spyware, adware. Even SPAM might be considered associated with malware, though not malware itself, since it can be the means by which hackers get those other types of programs onto your system.

Viruses

Viruses and worms function in the computer world much like they do in the real world in that they replicate themselves and pass from one carrier to another (be that a computer or a person, depending on which type you're talking about). They can either spread on their own, or after the user takes some pre-determined action like opening an email, running a program, etc. It turns out that most of these programs are written to take advantage of Microsoft Windows Operating system rather than Macs or Unix/Linux systems. But that has a lot to do with the fact that there are many more Windows users than other types of operating systems.

Trojans

Trojans get their name from the famous story of the Trojan Horse and operate in a similar fashion. Trojans get onto your system and hide there by appearing to be something else, a seemingly harmless file that when run, contains a "little extra something" that the user definitely isn't expecting. The end result varies depending on what's "inside the horse", to continue the analogy. It might be a program that deletes everything on your C: drive, it might install another program or change an existing program. This is how spyware is passed along much of the time. For instance, you download a free screensaver, install it and at the same time, also install a program that monitors your keystrokes and sends that info back to a third party via the internet.

Spyware and adware

Spyware and adware are among the biggest threats now. They also create the biggest headaches for security experts since so many computer problems are now found to be caused by spyware. Spyware creators are usually motivated by profit rather than purely malicious desires as might be the case with a virus/worm creator. Spyware and adware are typically used to control a computer and drive the user to websites which the creator will profit from or for displaying advertisin via popups, popunders, or other means.

Spyware is usually installed as part of another software package without the user's consent, or sometimes with their consent though they may not realized it. Often times, this implied consent is buried in the End User License Agreement (EULA) which the user must agree to prior to installing the program. By not reading or understanding the terms contained in the EULA, the user might be unintentionally agreeing to have spyware installed. Once installed, this might become a means for other spyware programs to also end up on that computer.

Worm

Worms operate a bit differently. These programs replicate themselves over and over again. Worms generally arrive through an email client. Machines become infected if the user accepts a Trojan file that contains a Worm in its payload. The majority of these programs are designed to exploit email address books stored on a mail server or hard drive. When you open a Trojan email attachment that contains a worm, the Trojan tells the worm file to propagate with all email addresses it finds and to email itself to each address, thus repeating the process.

The "Love Bug" is a good example of each of the above. It's a Trojan because it arrives disguised as a "Love Letter" when it is actually carrying a harmful program. It's a virus because once executed, it infects files on your computer, turning them into new Trojans. It's a worm because it propagates itself by sending itself out to everyone listed in your email address book or IRC client.

Bacteria

Bacteria programs are simply designed to replicate themselves many times, thus causing a lack of resource or slowdown of the computer.

Botnet

Similar to Spyware, Botnet applications are designed to copy software programs installed on individual computers and network computers within companies and organizations. Once a network has been exploited, the Master Botnet will usually command the Botnets that are located on the rest of the network and implement actions from the central server.

By James Hurst & Kevin Nelson

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