Malicious Software


Viruses are malicious software that comes in various forms with different purposes. Although the term virus is often used to describe all malicious software, there are actually three types, based on how they propagate or spread, a Trojan Horse, Virus, or Worm.

A "Trojan Horse" is a program that looks like it is doing something good, but in reality it is doing something destructive. The user is usually tricked into installing it, thinking it will be useful. On the movie The Net there was a Trojan Horse. It looked like it was keeping the system secure, but in reality it was sending private information to people who were using this information to perform illegal acts.

A "Virus" spreads like a biological virus in that some type of contact is made, i.e. copying a file with a virus attached to it, using a floppy disk in a computer with a virus in the operating system, or running a program with a virus attached to it. They can be sent to your friends and coworkers without your knowledge, usually as email attachments from you. Some email programs, can block potentially dangerous attachments, but you should never depend on your email software to protect you. Don't open attachments if you are not expecting it, without talking to the sender first.

A "Worm" is a program that travels independently through a network. Most computers are networked, so these can do a lot of damage in a short time. Worms are different from viruses and trojans in their ability to spread without any human intervention. You don't have to open an email attachment or download a file to become infected with a worm. You simply need to be running a computer that is vulnerable to one of the techniques that the worm uses. A few years ago, the Nimda Worm caused all kinds of havoc on many computer systems at Utah State University and other networks all over the world.

Virus protection software will protect your computer and stop most viruses. Virus protection data files should be updated daily to ensure that the latest viruses are being stopped. New viruses are always being created and virus definitions are needed to identify new viruses to antivirus programs. Most antivirus programs can be set to update their data files automatically, so you should take advantage of this feature. Often viruses will spread rapidly before the antivirus vendors have time to release a patch for it, so you should still be careful and not rely on your antivirus to protect you 100%. It is never legal to create a virus, even if it is not harmful. Viruses are created in many different ways. One common way is to use any program that has macro capabilities.

The following are just a few antivirus products that could be installed to help protect yourself:

  • McAfee (free to USU students and staff at, which can be accessed on campus or through the VPN or Proxy servers - call the Helpdesk if you need help setting up the VPN or Proxy server off campus)
  • AVG (free for personal use at
  • Norton (one year version often included on new computers)


Recently, a new category of malicious software has emerged, called spyware or adware. This software may be installed in various ways, but once it is installed, rather than destroy the contents of your computer like a virus is designed to do, it watches what you do and steals information or causes ads or other undesired programs to run on your computer. Many times users become infected, but they never know there is a problem other than that their computer is running a little more slowly than normal or that occasionally ads pop up on their computer.

There are various free utilities that can be installed in addition to your virus scanner, to protect yourself against spyware, including:


Operating Systems need to be updated often. Windows and most other operating systems can also be set to install updates automatically. Updates may be released daily, weekly, or monthly, and may vary in importance; it is good practice to set your computer to update itself automatically every day to make sure no important security fix gets missed. will detect needed or recommended updates, download them to your computer, and install them at your discretion. If you use another Operating System, it should be able to do the same. Regardless of your OS, set it to update daily.


A firewall is a security device, either hardware or software, that blocks unauthorized users from connecting to your computer via your network or Internet connection. Network firewalls are usually installed and maintained by network managers. Home computer users can install personal firewalls to secure their PCs and data. Firewalls often take some time to get configured properly and sometimes conflict with other software, but it is worth taking the time to set it up right.

A firewall should be set to block everything. If a program is not running properly, you may then open an exception in the firewall for that specific program; if you stop using it or use it infrequently, you should turn the exception off. If you need to communicate with a specific computer, you may open an exception to allow only that computer to communicate with you, leaving the rest of the Internet locked out.

Windows XP includes a firewall, but make sure your OS updates are installed to keep it up to date. ZoneAlarm [download] is a good firewall that is free for personal use. Other Operating Systems may have a built-in firewall or third-party firewalls that can be installed.