A virus is a malicious code or software which usually infects a computer without permission or knowledge of the user. Viruses can cause unexpected and undesirable damage to the computer if it is not adequately protected.

Here are some precautions to follow to protect your computer:

1. Always ensure that you install an effective anti-virus software from an established vendor. Scan your computer regularly
2. Always ensure that you update the virus definition or signature file in your computer regularly
3. Do not download any file or software from sites which are of unknown origin
4. Delete junk or chain emails. Do not open email attachments from unknown senders