Never put a disk from an unknown source into your computer.
Never open an attachment you receive via e-mail, unless you are expecting the attachment from a trusted source.
Make sure that others who use your computer do not put a disk from an unknown source into your computer or visit a website that could expose your system to a virus.
If you have a program you'd like to install on your computer, and you aren't 100% sure the new program is virus-free, check with your department's computer/ technical support person before you proceed with installation.
Use an up-to-date antivirus program, preferably one that also scans for Trojan horse programs. Scan all files coming into your computer.
Don't use illegal (pirated) copies of software. The program could have a virus or Trojan horse.