Postcard VIRUS - Snopes confirms
 

The name Hallmark is mentioned, but others seem to be listed in the circular I've just received.

Snopes lists several and mentions the Hallmark brand. It seems it hits the vital sectors on C: and is unrecoverable.

Fake or real?
 

The one that is a fake contains a warning only, and asks you to copy it to everyone you know. It is set up for the express purpose of harvesting email addresses.

The one that is real seeks to emulate the form of "so and so has just sent you an electronic greeting card, follow this link to receive it" or has the card in an attachment. Either following the link or opening the attachment will introduce you to the virus.

For more details see POSTCARD or POSTCARD FROM HALLMARK Virus Hoax - Netlore Archive

This warning has been circulating for years, take it with a grain of salt.