Open this malware or I'll sue...
"Hello. Your email is sending spam messages! If you don't stop sending spam, we will be impelled to sue you! We've attached a scanned copy of the document assembled by our security service to this letter. Please carefully read through the document and stop sending spam messages. This is the final warning!
Subject lines include "You are sending ad messages", "We are going to sue you", "This is the final warning", "We've sent you a copy of a complaint" and "A message from our security service".