There are all sorts of things you can find in your e-mail box. In the "destructive" and/or "annoying" category go e-mail attachments that contain:
- Trojan horses
In many cases, e-mail viruses are not "true" viruses because they cannot replicate without human interaction. Nonetheless, they have been very effective at shutting down major e-mail systems. See How Computer Viruses Work for details on viruses.
A Trojan horse, aptly named after the seemingly harmless tool of destruction in Homer's Iliad, secretly carries often-damaging software in a "plain wrapper." The plain wrapper is normally an e-mail file attachment from someone you may or may not know. The file attachment name itself can also be very misleading. When you run the attachment, it can do all sorts of things, from erasing files to changing your desktop. It then sends itself along to other people in your address book so that it can propagate itself.
Here are two examples to help you understand how e-mail viruses work. According to this page from Symantec:
See also this page for details.
Symantec offers more technical information and explains what you need to do if you suspect Worm.ExploreZip is in your system.
In certain special cases, e-mail attachments can execute even without your interaction. According to this Symantec Web page:
Microsoft has more information on this worm.
Keep your virus software up-to-date with the latest virus signatures from the software vendor, since the anti-virus software cannot detect new viruses without an update. If you use Norton AntiVirus software, ensure that Auto-Protect is enabled. Current Norton AntiVirus software automatically alerts you when your virus signature files are over 30 days old. Norton's LiveUpdate can also automate updating.
If you think a virus has infected your PC thanks to an e-mail virus that mails itself to people in your address book, call those people and tell them not to open the messages or attachments -- that is the only effective way to stop the spread.
These links will help you learn more: