Players who didn't have a Uplay Passport for Assassin's Creed 4 can get a code for free on Xbox Live Marketplace and PlayStation Network. After the game, it will never make another appearance in any Ubisoft game.
The publisher explained, "The Uplay Passport program was initiated as a means of giving customers full access and support for online multiplayer and features, along with exclusive content, bonuses and rewards. However, games today are blurring the line between offline and online, between what is “single player” and what is “multiplayer.” Based on that and on the feedback we received from you, we recognized that Passport is no longer the best approach for ensuring that all our customers have the best possible experience with all facets of our games."
Assassin's Creed 4: Black Flag was released two days ago on Xbox 360 and PlayStation 3. It will be arriving on PC soon.