From HTTP over X.509 - Office 2007:
"Proof of Concept:

A signed Word 2007 document that triggers an HTTP request is available at
http://www.klink.name/security/HTTP_over_Office_2007_PoC.docx
The document contains a link which shows the last 10 HTTP requests
triggered by this document. By verifying whether you are on the
list, you can verify if you are affected by this vulnerability."

Sometimes I wonder why a text editor should be allowed to open tcp connections :-/
Next time, guys, go with GnuPG.