The release date for Assassin's Creed 4: Black Flag was accidentally revealed through the game's website due to a glitch. Ubisoft has since removed the date but not before gamers saw it.
AC4 will be launching on October 29th. That day is a Tuesday so it might only apply to North America. Europe will presumably receive the game on Friday, November 1st.
Ubisoft announced AC4 for the Xbox 360, PS3, PC, and Wii U yesterday. The official website - before it was edited - mentions that the game will be coming to next-gen consoles as well. The vagueness there is probably due to the fact that the next Xbox hasn't been formally announced yet.
The revised website now has a countdown to Monday. On that day, we'll find out a lot more about the game. We'll also get to see the first trailer.
AC4: Black Flag focuses on piracy in the Caribbean. Ubisoft stated previously that the game features a different hero and setting than other AC games.
