Email scam warning - "Undelivered package" message

Beware of an email saying:

Dear client,
Your package has been returned to the Post Express office.
The reason of the return is "Error in the delivery address"
Attached to the letter mailing label contains the details of the package delivery.
You have to print mailing label, and come in the Post Express office in order to receive the packages.
Thank you.
Post Express Support 

Downloading the "label" actually installs a rather nasty virus on your PC.

This version of the message has just been received locally, but there are others about claiming to be from different companies. Beware!