Stockade is a term to describe a kind of military fortress. Since the beginning of mankind, in any warfare, many are the tactical, logistical, strategies and equipments used against the opponent, which even considering that they are used either in separated as well as in a combined constraining action, they are setting to the time involved in the military operations. However, in the secrete warfare, hereinafter named as the invisible stockade being more subtle, it never ends.
Thus during the smouldering or declared wars it performs behind the enemy lines through, sabotage, guerrilla operations, political upheaval, forcing decision by psychological constraining terrorism plots and standard intelligence procedures.

Sabotage, political upheaval, data collecting behind enemy lines never ends. To stop as much as possible such enemy subtle and stealth operations, security agencies tried by all mean in training the society to avoid reveling relevant information on the country war efforts. Generally such espionage countermeasurers are taken throught the publication of warning posters, notes spread all over the nation public places or even in local made products such as, books, tools etc, similar to the enclosed one printed in the USA during the WWII days.
By other hand in the peacetime, its purpose consists to fight against the enemy by stealing his secrets as well as in destroying his morale. The invisible stockade is as old as mankind. One of its oldest and well-known stratagems is the tale of the "Trojan Horse". After ten years of fruitless military efforts, the Achaeans realized that Troy perhaps could be taken by cunning instead of by force, and this insight invited them to construct a wooden horse, which was to become the instrument of their victory. They let an armed force hide itself inside the horse, and in order to induce the Trojans to bring it within the walls, they left it abandoned in the plain, feigning retreat after engraving on the horse a treacherous inscription:" For their return home, the Achaeans dedicate this thank-offering to Athena - the wisdom's goddess
Moved by curiosity, the Trojans brought the wooden horse within the city's walls and at night suddenly the hidden armed force attacked them.
To let one know the great influence of such subtle but fateful stratagem, even today, in the digital era, taking advantage of the same treacherous connotation of the Achaean tale, one of the most notorious and devastating virus ever produced in the Internet is named as the Trojan horse. When it is spreaded in the net through a naïve e-mail messages, it causes tremendous deleterious consequences for companies and users.

The world well-known stratagem: the wooden made Trojan Horse.
Courtesy Warner Brother.

Thus, the episode of Trojan horse gives one the idea of the entrails of this subversive war tactics, generally surrounded by complete secrecy and known to only a small number of persons, whose operational structure is based fundamentally in communication.