Pepsi Invaders (also known as Coke Wins) is an advergame for the Atari 2600 platform, based on the popular Space Invaders. It was commissioned by Coca-Cola for their 1983 sales convention, and developed by Atari as a modification of the original Space Invaders cartridge (essentially, an official ROM hack).
The game is a modification of Space Invaders, with each row consisting of the letters P E P S I followed by an alien, instead of the original six aliens.
In addition, the game was changed from having limited lives but unlimited time as in the original Space Invaders, to having unlimited lives but a three-minute time limit in which to shoot as many of the enemies and complete as many levels as possible.
Source: Wikipedia, "Pepsi Invaders", available under the CC-BY-SA License.