What was the first .hack game?

The first hack game was ".hack//Infection" because it was the initial installment in the ".hack" series, introducing players to the fictional online game called "The World." This game was unique as it blended traditional role-playing elements with a simulated online multiplayer experience, allowing players to delve into a virtual world filled with mystery and danger. ".hack//Infection" set the foundation for the rest of the series, showcasing its innovative storytelling, immersive gameplay, and distinctive cyberpunk aesthetics.