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Viruses
A Virus is a piece of programming code usually disguised as something else that an unwanted and undesirede event to happen to your computer. It is usually designed so that it automatically spreads to other computer users. They can be transmitted as attachments to an e-mail, downloads, or be present on a diskette or CD and the source is often unaware of the virus. Some viruses start their effect as soon as their code is exectued while other viruse lie dormant until cirumstances cause their code to be executed by the computer. Some viruse are playful in intent and effect. For example, you might receive an email with the subject, "You Have A Crush" or "I Love You". You may be curious and want to know WHOM the email is from and once you open it the virus takes effect and some can be quite harmful, erasing data or causing your hard disk to require reformatting.
There are three types of viruses:
1. Macros- the most common viruses, and they usually do the least damage. Macro viruses infect your software applications and typically insert unwanted words or phrases.
2. File Infectors- these attach themselves to program files, usually selected .COM or .EXE files. Some can infect any program for which execution is requested.
3. System or Boot-Record Infectors- These viruses infect executable code found in certain system areas on a disk. They attach to the DOS boot sector on diskettes or the Master Boot Record on hard disks.
Its difficult because the best protection against viruses is to know the origin of each program or file you load into your computer or open from your e-mail program. you can buy anti-virus software that can screen e-mail attachments and also check all of your files periodically and remove any viruses that are found.