For those who do not recall the story, the Trojan Horse was a present – a giant wooden horse – given from one army to another as a token of peace and of respect. The recipient army however had housed themselves in an impenetrable fortress, and this had brought about something of a stalemate. Of course then the large wooden horse was not a gift at all, but a container housing many members of the opposing army, all of whom would jump out and attack those in the fortress. The genius was that shaped like a gift, the defending army actually accepted the carrier into their gates and left it unattended so that they could bide their time to do their damage.
While corporate gift ideas are no where near as dramatic, and while no one would in their right mind accept a huge wooden horse as a corporate gift anyway, the central concept is the same and this is the first example from which you can learn a lesson.