There is a kind of message in espionage that is meant to be intercepted by an adversary for the purpose of spreading false information: For instance, by sending a letter stating that troops are moving north when they're really moving west. As an example, this tactic was used by the British during the American Revolutionary War, according to the National Library for the Study of George Washington website.
British Generals Burgoyne, Clinton, and Howe, several times during the war, created letters with false information that they hoped would fall into American hands. They hoped the Americans would be deceived by the information.
I'm wondering if there is a word to describe this kind of message, colloquial or otherwise. My initial research centered around the term false flag, but that term refers specifically to disguising an activity by making it appear to have been carried out by a different party.
Is there a term of any kind that means "a message sent that is meant to be intercepted by an adversary for the purpose of spreading false information?"
An example sentence would follow from the description above:
Though the letters appeared to describe British troop movements, they were ______, giving Washington an inaccurate picture of the battle lines.