Details are still pretty much missing but Bethesda have launched a Fallout teaser site that points to tomorrow for something – presumably a reveal or announcement of Fallout 4. Hidden in the source code for the site is a little bit of a hint:

PA System failure has occured.

Shutdown of the masterbrain has been authorized and all sensitive materials have been removed for safety purposes.

Please attempt re-access. Have a pleasant day.

It's not much to go by but Masterbrain was a Fallout 3 character that inhabited the Vault-Tec headquarters and controlled all the other security robots in the building in the year 2277. Make of it what you will but it might point towards a timeframe for when the game takes place and what the subject material might be. Or it might just be something hidden to please the fans who went digging.

Either way, stay tuned for an update tomorrow, when we'll cover whatever the announcement is. We're all chomping at the bit to find out what it is.