First. If you receive an email from someone warning about a virus and asking that you forward to everyone that you know, it's probably a hoax.
Be sure to check one of these useful hoax information sites
Email used to be fairly secure, the preferred means of spreading virus was via downloaded software. In the last couple of years email has been the method that virus writers have chosen to spread their malicious programs. Some of the virus writers have an extreme dislike for Microsoft products, so their target of choice has been Microsoft programs, most noticeably Outlook and Outlook Express.
Outlook/Outlook Express viruses The latest round of Viruses modify your system in some way, then send email to everybody in Your addressbook a message trying to entice them to open the document. When the person opens the document, their system become infected with that virus. If that person uses Outlook, then their computer sends to everybody in their addressbook, etc. etc. The big problem here is that you send the people in your addressbook the virus. The people that receive the virus assume it's safe to open since it's from somebody they know, that's how these virus spread. A good rule to follow is Don't open the attachment unless you are expecting it.
Don't assume that GIF and JPG files are safe. Windows has a 'feature' to not display 'known file types'. Files have a 3 digit extension that identifies the file type to the system. An image file may have the .jpg or .gif extension. ie. vacation.jpg
This in theory would be a picture of your vacation. If windows knows what a .jpg file is, it wouldn't show the .jpg part, windows would just show 'vacation'. The problem here is, if I were to send you a .vbs file (visual basic script) called vacation.vbs , windows if it knows the file type would hide the .vbs part. One step further here. If I were to send you the same .vbs file but call it vacation.jpg.vbs (this file name is a legal file name), since windows knows what a .vbs is, would just show: vacation.jpg (hiding the .vbs part) This is where the virus writers sucker people in. The person that receives it assumes it's a .jpg file and opens it. score: Virus 1 victims 0.
To try this out, create a new notepad document. Enter some text, then click on 'file/save'. Save the new document to the desktop, call it 'blah' Now do 'file/save as' and call it blah.jpg
Look on the desktop now, there should be a new file that says blah.jpg and one that says blah. It may seem obvious that they are both 'text' files, but when you receive the attachment, it may not be so obvious.
you can disable the feature to hide know file types. Open up 'my computer', from the menu bar select 'view/folder options'. select 'view' look for 'hide file extensions for known file types'. uncheck it. You should be able to look on the desktop and see the files you created earlier. This time they should be called 'blah.txt' and 'blah.jpg.txt'. Now, if you look at attachments, they should reflect what they really are. vacation.jpg, and not vacation.jpg.vbs.
However, This does not mean that it's safe to open attachments. You should never open an attachment unless you are expecting it
Hopefully, the person that is sending the attachment has told you that they are sending it before they send it. Preferably via some 'voice' mechanism first. I'm guessing that the next generation of virus will send an email telling you to expect an attachment then to actually send the attachment.
Just because you don't use Outlook doesn't mean that your system isn't infected. Outlook is the means of spreading the virus. You can still infect your system.
Virus protection software can only protect you from viruses that it knows about. Just because you have installed a virus detect program doesn't protect you. You need to update the 'virus definitions'. Most anti-virus companies update their defs every couple of weeks or so.