Apple has confirmed maybe the worst kept secret in Silicon Valley: it’s been working on a cloud service, and will announce it at the June 6 Worldwide Developers Conference.

So now we know annual developer’s conference will unveil “iCloud®, Apple’s upcoming cloud services offering,” but we don’t know yet what it is, or what exactly will reside at the domain name it may have bought for $4.5 million in April.

iCloud could be the mythical iTunes streaming service, a possibility that is looking increasingly likely now that Apple has most of the major record labels signed up for it, in a space pioneered by Amazon and Google, which has no such deals. Or it could be Apple’s version of DropBox, the amazing sync and storage service that currently glues together the whole iOS ecosystem along with its desktop service.