By Tricia Hopper

MISSISSIPPI STATE -- As more people begin using personal computers, they quickly learn that computer viruses are hard to avoid.

Dan Brook, head of Mississippi State University's Computer Applications and Services department, said computers are infected by viruses primarily through e-mail attachments.

"Typically, people will receive e-mail that looks legitimate, and they will open the attachment to release it on their computer," Brook said. "A software code is embedded in these attachments that is designed to do anything from rearranging icons to completely destroying the information on the computer system."

Typically, a victim must open an e-mail attachment to get infected with a virus, but other forms of destructive software can enter your computer through other avenues. In some cases, all the user has to do is visit a Web site.

"Computer viruses are extremely common, and all systems are susceptible," Brook said. "However, some types of systems are not targeted as frequently, such as the Macintosh."

The recent Blaster worm is a form of destructive software that needs only to find a computer connected to the Internet through a local area network or dial-up connection. Brook knows first-hand the havoc Blaster can cause as it invades computer address books and then e-mails the virus code to everyone on the contact list. He oversees the MSU Extension Service's 1,500 computers and had a large number of them infected.

Virus: A virus is computer programming code that makes copies of itself without any conscious human intervention. Some viruses replicate themselves, display messages, and install or delete other software or files. A virus requires the presence of some other program to replicate itself. Typically viruses spread by attaching themselves to programs or file formats.

Worm: A worm is a virus that does not infect other programs. It makes copies of itself and infects additional computers (typically by making use of network connections) but does not attach itself to additional programs; however a worm might alter, install or destroy files and programs.

Trojan Horse: A Trojan horse is a computer program that is hidden inside another program or that masquerades as something else to trick potential users into running it. A program that appears to be a game or image file may perform some destructive function. A Trojan may spread itself by sending copies of itself from the host computer to other computers, but unlike a virus it usually will not infect other programs.

Until solutions, or patches, were made available, Brook recommended all Extension computers be unplugged from the Internet to help stop the spread of the worm and prevent further damage. Symptoms varied from error messages to sluggish responses to infinite reboot loops.

Once the worm attacked systems computer hackers opened "back doors" to a few computers on campus and invaded them at their leisure. The damage remains a factor as computer personnel work to reload software on every Extension computer to remove possible hacks into systems and help avoid problems in the future.

"A virus can spread exponentially, and Blaster is one of the most devastating to hit the Internet," Brook said. "If a person has 100 contacts, and then those hundred people each have 100 contacts in their address book, the virus easily spreads to thousands in a very short time."

A vast number of increasingly complex viruses now threaten computers. For example, a Trojan horse attacks with a "ticking time bomb" effect. Once it has accessed a computer, the virus remains dormant until a specified date that is embedded in its code.

"At the set date and time, it activates to perform whatever destructive assignment it was devised for," Brook said. "Because the virus remains dormant for a while, it is difficult to find or determine the source."

E-mails often bring dire warnings about viruses and may encourage computer users to remove certain files from their computers. Many of these messages are hoaxes or chain letters. While hoaxes do not automatically infect systems like a virus or Trojan, Brook said they are time consuming and costly.

One such virus is the Teddy Bear virus, which is especially deceiving because it comes from an address in the recipient's address book. The message warns of a possible virus that can only be stopped if a certain file is immediately deleted.

"Trying to avoid the virus, individuals will delete the file as instructed in the e-mail, which in most cases is actually a file the computer needs to function," Brook said. "This crashes their computer system and makes it inoperable until the systems software is reloaded."

Spyware is a new and worrisome form of software attack. A computer code captures keystrokes and gathers important information, such as online banking figures, social security numbers and credit card numbers, without the user ever knowing, Brook said. Users inadvertently download Spyware with common music file-sharing programs such as Gator and Kazaa.

"Be extremely wary of pop-up advertisements that you have to click on to view. You could be downloading Kazaa, Gator or Spyware and not even know it," Brook said.

Several methods of protecting computer systems exist, including hardware and software firewalls, which limit network access and decrease the chances of getting a virus or worm. Users can purchase programs that screen all information coming into or going out of a computer. But Brook said sensible, cautious users can avoid most viruses often without spending any money.

"The best form of protection is prevention," Brook said. "Be suspicious of unrecognizable e-mails, especially attachments. Simply deleting e-mails from unfamiliar addresses will help avoid common viruses. Installing anti-virus programs on computers will help catch viruses before they attack."

Most computers purchased today include anti-virus programs, but users do not realize it is available or important. Updating these programs regularly will significantly reduce unwanted viruses.

Regularly downloading Windows Update can reduce the possibility of computer attacks. Installing update patches on the computer system scans and plugs "holes" where hackers could get into the system.

"These holes are found in the millions of lines of coding in the Microsoft Windows operating system, so it's relatively easy for a hacker to find a hole and use it for his or her benefit," Brook said.