Beware of Greek bearing gifts.
An allusion to the story of the wooden horse of Troy, used by the Greeks to trick their way into the city. It is recorded in Virgil's Aeneid, Book 2, 19 BC:
"Do not trust the horse, Trojans. Whatever it is, I fear the Greeks even when they bring gifts."
How its used today:
it was resurrected in a sideways reference during a 1990s copyright dispute. There was considerable discussion then, in Internet chat rooms etc.