Malicious code can take forms such as a virus, worm or Trojan. It can hide behind an infected web page or disguise itself in a downloadable game, screen saver or email attachment.

Computer viruses are programs that spread or self-replicate. They usually require interaction from someone to be activated. The virus may arrive in an email message as an attachment or be activated by simply opening a message or visiting a malicious web site. Some viruses consume storage space or simply cause unusual screen displays. Others destroy information. If a virus infects your PC, all the information on your hard drive may be lost and/or compromised. Also, a virus in your PC may easily spread to other machines that share the information you access.


Viruses can exhibit many different symptoms. If your computer behaves erratically, employees are advised to contact their organization computer support representative. At home, disconnect the PC from the Internet and run a full virus scan.

  1. Check that your anti-virus software is updated at least every week or set it for automatic updates. New, fast spreading worms and viruses are released every day.
  2. Before implementing or using software from any source, check it for viruses with a current virus scanner. Employees, if you do not have a virus scanner installed on your PC, call your organization representative.
  3. Store removable media as CDs/thumb drives/diskettes as "write protected" whenever possible to prevent infection by viruses.
  4. Do not load free software on your computer from an untrusted source.
  5. Consider blocking extensions such as: .bat, .cmd, .com, .exe, .pif, .scr, or .zip through content filtering software.
  6. Depending on the extent of the infection, you may need to re-install your operating system.


Worms are similar to viruses because they self-replicate, however, they do not require any user interaction to be activated. Worms spread because of vulnerabilities or "holes" in software.

  1. Install either a software or hardware firewall. A well configured firewall can stop propagation of a worm.
  2. Anti-virus software will often detect worms. Keep your anti-virus software up-to-date.
  3. Know where to find your anti-virus vendor's "rescue" web site for your home computer.
  4. Keep your PC and servers "patched."


Trojans (also known as backdoors) are malicious code hidden in a legitimate program that, when executed, performs some unauthorized activity or function. This can range from stealing your password and credit card information to allowing someone to take control of your computer. To prevent installation of Trojans on your machine:

  1. Run anti-virus software on your desktop and follow the best practices for using it.
  2. Be careful about downloading games, screensavers and other files. Download only from trusted Internet sources.
  3. Be careful about file and music sharing services because you can inadvertently share files you did not intend to share. Downloaded files can contain viruses and other malicious code.

Denial-of-Service Attacks

Denial-of-service attacks are an assault upon a network or web site that floods it with so many additional requests that regular services are either slow or completely interrupted. In some instances, a group of remotely controlled, compromised desktops are combined to jointly attack a target system.


Hoaxes are email messages that resemble chain letters, offer free money, or contain dire warnings and offers that seem to be too good to be true. If you receive a hoax via email, delete it. Sharing hoaxes slows down mail servers and may be a cover for a hidden virus or worm.