If you get an email saying "e-card from a friend", "e-card from a colleague", etc; don't open it, but mark it as spam and delete it. (Some email providers delete an email automatically when you mark it as spam.) It is likely a virus called the storm worm or Peacomm trojan. Gotta see to believe? Search "e-card spam". The two articles below are from earlier this month. [http://www.informationweek
Now, if you receive an e-card that is from someone you know - it has his/her name in the email's title. For example, you get an email with the subject "John Brown sent you an e-card" You should contact John to make sure he sent you an e-card. If he did, then it's probably safe to open. Note that a real e-card will not try to download a .exe file to your computer. A real e-card will open in your Internet explorer or other web browser window.
Bottom line: be very careful what emails you open.