Military deception
Belgian authorities discounted this true information as false because of the ease with which they obtained it.

Multiple Forms of Surprise: Friendly events about which an adversary can be deceived are described in the mnemonic SALUTE-IS, which stands for Size, Activity, Location, Unit, Time, Equipment, Intent, and Style. The maxim indicates that the more of these categories the friendly side can deceive the adversary about, the more likely the adversary is to believe the deception. Conversely, if there are plans and activities about which the adversary is already aware, attempting to deceive him about them is unlikely to succeed. In Operation Bodyguard, the Germans knew there would be an invasion on the coast of France, that it would happen in 1944, and that it would be based in England. They did not know the exact date and the exact location. The Allies concentrated their deception on the SALUTE-IS details the Germans did not know about, and did not attempt to deceive them about what they already knew.

Planning process: The doctrine for planning deception has been codified over time. In the U.S. military, this doctrine begins with understanding the deception target's cognitive process. Expressed as "See-Think-Do", this understanding of the adversary considers what information has to be conveyed to the target through what medium for the target to develop the perception of the situation that will cause the enemy to take an action beneficial to the friendly side. In the planning process, "See-Think-Do" is considered in reverse order—what does the friendly side want the enemy to do as a result of the deception, what perceptions will the target have to form to take the action, and what information needs to be transmitted to the target through which medium so that the target will develop the desired perception.
As an example, the intent for Operation Bodyguard was for Germany to allocate forces away from Normandy ("Do"). The perception the Allies wanted to create in the mind of the deception target (Hitler) was that the Allies were planning to invade at Calais ("Think"). The information the Allies conveyed to the target to create the perception included the false radio traffic, dummy equipment displays, and deceptive command messages of the fictional First United States Army Group ("See").

History: 

Ancient Egypt: According to a story from an ancient Egyptian papyrus, in about 1450 BC, an Egyptian army under Pharaoh Thutmose III and his general Djehuty besieged the Caananite city of Yapu (later Joppa and now Jaffa). Unable to gain entry, they resorted to deception. Djehuty hid several soldiers in baskets and had the baskets delivered to the town with the message that the Egyptians were admitting defeat and sending tribute. The people of Yapu accepted the gift and celebrated the end of the siege. Once inside the city, the hidden soldiers emerged from the baskets, opened the city gates, and admitted the main Egyptian force. The Egyptians then conquered the city.

Ancient Greece: The Iliad and The Odyssey, epic poems composed between the 9th and 6th centuries BC, are credited to the Ancient Greek author Homer. These poems contain details of the Trojan War, presumed by the Greeks to have been fought in approximately the 13th century BC. The Odyssey provides the details of the Trojan Horse, a successfully executed deception. After several years of stalemate, a Greek leader, Odysseus, devised a deception. Over three days, the Greeks constructed a hollow wooden horse, which they inscribed as an offering to the goddess Athena in prayer for safe return to their homes. The Greeks then pretended to depart the area around Troy, giving the impression that they had sailed for Greece. Rather than risk offending Athena, the Trojans brought the horse into the city. That night, Greek soldiers concealed inside the horse came out of their hiding place and opened the city gates. The main force of Greek soldiers who had actually remained nearby then entered the city and killed the inhabitants.

Ancient Macedon: In 326 BC, the army of Macedon, which was led by Alexander the Great, had advanced through the Middle East to Asia, conquering numerous kingdoms along the way. Alexander planned for battle against the forces of Porus, the king of the region of Pakistan and India that is now Punjab. To confront Porus, Alexander needed to cross the Hydaspes River. Porus used the terrain to his advantage and arranged his forces to prevent Alexander from crossing the river at the most likely fording point. Leading up to the battle, Alexander scouted several alternative fords, but Porus moved each time to counter him.
Alexander eventually located a suitable crossing point approximately 17 miles north of his base. He then led a portion of his army to the crossing site, while his subordinate Craterus kept the entire army's campfires burning within sight of Porus and feigned several river crossings that Porus was able to observe. With Porus distracted, Alexander successfully led his detachment across the river, then marched south to engage in battle. In the Battle of the Hydaspes, Alexander's army had the element of surprise and quickly defeated Porus' troops, while sustaining relatively few casualties on the Macedonian side. Having conquered Porus' kingdom, Alexander then allowed Porus to rule it as one of Alexander's satraps.

Ancient China: In 341 BC, troops under the general Sun Bin of the state of Qi faced battle with the forces of the state of Wei. Knowing that Wei regarded the army of Qi as inferior and cowardly, Sun Bin decided to use Wei's perception to his advantage. When Qi's forces invaded Wei, Sun Bin ordered them to light 100,000 camp fires on the first night. On the second night, they lit 50,000. On the third, 30,000. Sun Bin's deception caused the Wei forces led by general Pang Juan to believe Qi faced mass desertions. Rushing to attack what they believed to be an inferior army, the Wei forces assaulted Qi's troops at a narrow gorge, not knowing Sun Bin's soldiers had prepared it as an ambush site. When Pang Juan's troops reached the gorge they observed that a sign had been posted. Lighting a torch to see the message, the Wei commander read "Pang Juan dies beneath this tree". The lighting of the torch was the signal for Qi to initiate the ambush. Sun Bin's army quickly routed Pang Juan's and Pang Juan committed suicide.
Another well-known deceptive measure from ancient China has come to be known as the Empty Fort Strategy. Employed several times in numerous conflicts, the best-known example is a fictional one contained in a historical novel from the 1320s AD, Romance of the Three Kingdoms. This work, which contains embellished tales of actual Chinese history from 169 to 280 AD, includes the story of general Zhuge Liang of Shu Han employing the Empty Fort Strategy. As recounted in the novel's description of Zhuge Liang's Northern Expeditions, an actual historical event, the forces of general Sima Yi of Cao Wei arrived at Zhuge Liang's location, the city of Xicheng, while the bulk of Zhuge Liang's army was deployed elsewhere. Zhuge Liang instructed the few troops he had on hand to pretend to be townspeople and told them to perform tasks which would make them visible to Sima Yi, including sweeping the town's streets. Zhuge Liang ordered Xichneg's gates to be opened, then took up a visible position on a viewing platform, playing his Guqin while flanked by only two pages. Because Zhuge Liang's reputation as a military leader was so great, Sima Yi assumed Zhuge Liang had prepared an ambush, so he declined to enter Xicheng. Zhuge Liang's deception saved the town and prevented the few soldiers he had with him from being massacred or taken prisoner.

Ancient Carthage: During the Second Punic War, the Carthaginian general Hannibal employed deception during the Battle of Cannae in 216 BC. In preparing to face a Roman force led by Lucius Aemilius Paullus and Gaius Terentius Varro, Hannibal had 40,000 soldiers, as compared to the over 80,000 that had been amassed by Rome. To overcome the Roman advantage in numbers, Hannibal placed his less experienced and disciplined Gauls in the center of his formation, arranged to bulge out towards the Romans. On either side of his line, Hannibal positioned his experienced and disciplined Libyan and Gaetuli infantry. Hannibal intended for the Gauls to give way to the advancing Romans, with the center of his line bending but not breaking. Seeing the Gauls appear to retreat, the Romans would advance into the bowl shape or sack created by the bending of Hannibal's line. Once inside the sack, the African infantry positioned on the left and right would wheel inwards and attack the Roman flanks. In combination with the Carthaginian cavalry, the infantry on the flanks would continue moving until they encircled the Romans and could attack their rear. The battle unfolded as Hannibal had envisioned. Only 10,000 Romans escaped, with the rest either killed or captured. The battle came to be seen as evidence of Hannibal's genius for tactical generalship, while it was among the worst defeats suffered by Ancient Rome.

Ancient Rome: During the Gallic Wars, in 52 BC Roman commander Julius Caesar attempted to engage the forces of tribal leader Vercingetorix in open battle in what is now central France.