Software that uses a variety of techniques to attempt to protect you from known and unknown viruses, worms, and trojans.
Existing viruses are recognised by certain text that appears within that virus. The content of the file to be checked is compared against a list of these virus signatures looking for a text match. In order to detect new viruses you must keep your virus signature file up to date. At a minimum you should check for updates every time you go on-line.
Don't view spam emails. In many cases viruses are attached to emails in such a way that just viewing the email is sufficient to trigger the virus. It is always possible that the virus is one that your anti-virus doesn't yet recognise or you haven't yet installed the update that will recognise it.
Turn off the preview pane in your email program to avoid having emails opened unless you want them open. If an email looks suspect then delete it without opening it.
Don't open attachments unless you know the sender and know that they sent it. Often viruses appear to have come from people you know. In many cases these viruses will have originated elsewhere and the supposed sender knows nothing about it. If you are not expecting the attachment then email the sender to confirm that they really sent it. This will protect you from worms and trojans wherever they came from but there is still a slight possibility that your friend may have actually sent you a file not realising that it contains a virus.
This article written by Stephen Chapman, Felgall Pty Ltd.