A general and not very precise definition is: it's a small program written purposefully to cause harm to a computer.
Keeping your Operating System up to date
Every time a security hole is discovered in the operating system (Windows XP), Microsoft releases a new critical update. It is very important that you install these critical update to avoid the hassle of your computer being attacked by viruses.
By default, your computer is set to download the critical updates automatically. The only thing you have to do is to install them. Whenever a little bubble comes up saying that 'New updates have been downloaded and are ready to be installed', click on that bubble and proceed through the installation process.
Before you start installing the updates, it is important that you save and close all your documents and close all other programs.
Keeping your virus definitions up to date
Symantec Antivirus installed on your computer should update itself automatically whenever you connect to Internet. New updates are generally released every Wednesday. You can check if your antivirus is up to date by doubble-clicking on
in your system tray in the bottom right corner of your screen. If the icon is not there, it may indicate that your computer is already infected. To update the virus definitions manually...
icon in the taskbar. Scanning and cleaning
icon in the taskbar.