Your computer may be infected with a virus. But, is it really a virus? Viruses, worms, and 
trojans may be the culprits. These words are sometimes used identically although they have different meanings. This monthly tip is dedicated to de-mystifying these terms so that you are aware of their meanings, causes, and effects.
Virus
Definition: A virus attaches itself to a program or file so it can spread from one computer to another, leaving infections as it travels. Almost all viruses are attached to an executable file, which means the virus may exist on your computer but it cannot infect your computer unless you run or open the malicious program.
Cause: A virus cannot be spread without a human action. The Internet is currently the main virus entry point. This is due to the enormous possibilities it offers for exchanging information (e-mail, browsing web pages, file downloads, chats, newsgroups, etc.). Other virus entry points are CDs, floppies, and networks.
Effects: Certain viruses deliberately damage files or the computer’s operation, while others just try to spread themselves around. Nevertheless, the ones that just spread themselves are just as harmful, since they damage files and may cause other problems in the process of spreading.
Worm
Definition: A worm is similar to a virus by its design, and is considered to be a sub-class of a virus. The biggest danger with a worm is its ability to replicate itself on your system, so rather than your computer sending out a single worm, it could send out hundreds or thousands of copies of itself, creating a huge devastating effect.
Cause: Worms spread from computer to computer, but unlike a virus, it has the ability to travel without any help from a person.
Effects: One example would be for a worm to send a copy of itself to everyone listed in your e-mail address book. Then, the worm replicates and sends itself out to everyone listed in each of the receiver’s address book, and the manifest continues on down the line. Due to the copying nature of a worm and its ability to travel across networks the end result in most cases is that the worm consumes too much system memory (or network bandwidth), causing network servers, and individual computers to stop responding. In more recent worm attacks such as the much talked about Blaster Worm, the worm has been designed to tunnel into your system and allow malicious users to control your computer remotely.
Trojan Horse
Definition: The trojan horse, at first glance will appear to be useful software but will actually do damage once installed or run on your computer. Those on the receiving end of a Trojan Horse are usually tricked into opening them because they appear to be receiving legitimate software or files from a legitimate source.
Cause: This type of program doesn’t copy itself but does do damage to your computer. These types of programs rely on people to pass them around and to run them. They do not e-mail themselves. The idea is to make the program look like it is something harmless, like a screen saver or joke, so it gets sent around.
Effects: When a Trojan is activated on your computer, the results can vary. Some Trojans are designed to be more annoying than malicious (like changing your desktop, adding silly active desktop icons) or they can cause serious damage by deleting files and destroying information on your system. Trojans are also known to create a backdoor on your computer that gives malicious users access to your system, possibly allowing confidential or personal information to be compromised. Unlike viruses and worms, Trojans do not reproduce by infecting other files nor do they self-replicate.
This is a crash course on the most popular infections. Make sure you have your anti-virus software updated to prevent viruses, worms, and trojan horses!