Here's the scoop on this hoax.  As usual, 99.9% of these are garbage.

Netlore Archive: Hoax email alert warns of 'the worst virus ever' circulating in 
the form of an attachment labeled 'POSTCARD'

Description: Email hoax
Circulating since: Feb. 2008 (this version)
Status: False

IMPORTANT NOTE: Some versions of this hoax claim the information was "verified" 
on Snopes.com. This is NOT true. There is verification on Snopes.com of a
different e-card virus threat with a similar name.

Email example contributed by Jenifer B., Feb. 9, 2008:

PLEASE FORWARD THIS WARNING AMONG FRIENDS, FAMILY AND CONTACTS!

You should be alert during the next few days. Do not open any message with an 
attachment entitled "POSTCARD," regardless of who sent it to you. It is a
virus which opens A POSTCARD IMAGE, which 'burns' the whole hard disc C of your 
computer. This virus will be received from someone who has your e-mail address 
in his/her contact list. This is the reason why you need to send this e-mail to 
all your contacts.

If you receive a mail called" POSTCARD," even though sent to you by a friend, do 
not open it! Shut down your computer immediately.

This is the worst virus announced by CNN. It has been classified by Microsoft as 
the most destructive virus ever. This virus was discovered by McAfee yesterday,
and there is no repair yet for this kind of virus. This virus simply destroys 
the Zero Sector of the Hard Drive.

Comments: With so many real viruses afoot these days bearing names almost 
identical to the nonexistent threats warned of in hoax messages, it is crucial 
to be able to distinguish between the real threats and the bogus ones.

Keep the following points in mind:

1. There are real viruses, trojans, and other forms of malware currently being 
distributed by means of spoofed (phony) e-card notices.  This means all users 
must be very careful when dealing with e-card notices, no matter what the 
apparent source. Before clicking on any links or attachments, check to see if 
you can verify that the notice came from a legitimate source -- it's not always 
easy. If you can't verify, don't click.

DON'T click on links or attachments in e-card notices that arrive anonymously, 
or from senders whose names you don't recognize.

DON'T click on attachments or links that seem suspicious in any other way.

2. In general, forwarded warnings such as the 'POSTCARD' alert above cannot be 
trusted to provide accurate information.
READ CAREFULLY! Don't confuse hoaxes with the real thing. Bogus virus warnings 
often contain links to websites which, at first glance, may seem to confirm the 
authenticity of the message, but which in fact discuss a completely different 
matter.

This is a case in point. Despite the fact that there are real e-card viruses, 
the "POSTCARD" warning above is, in fact, a hoax. It is simply the newest of 
many variants of a
hoax message circulating for the past several years (compare the texts and 
you'll see what I mean). Don't depend on this type of warning for protection, 
and avoid forwarding such messages to others unless you can confirm with some 
certainty that the threat they describe is real.

3. Protecting yourself from real virus and trojan threats entails a few simple 
but critical measures. Follow them religiously:
a. Always be very careful concerning which attachments you open and which files 
you download. If you can't be reasonably sure they are safe, don't open or 
download them.
b. Maintain up-to-date antivirus software
on your computer, configure it to detect trojan horses and other malware 
automatically, and scan for viruses and other threats regularly.
c. Always be careful concerning which links you click on, especially in messages 
from anonymous or unfamiliar sources. Clicking on these links can instantly
download malicious software onto your computer. Again, if you can't be 
reasonably sure a link is safe, don't click on it.

Steve, K8SP