Microsoft CEO Steve Ballmer announced during a keynote at BUILD that the company has sold over 4 million individual upgrades of Windows 8.

Microsoft has confirmed that BUILD 2012 has sold out, just under an hour after they opened up registration.

Just to remind everyone: Registration to Microsoft’s BUILD 2012 conference will be opening up today.

Microsoft has officially announced the BUILD 2012 conference, which will be taking place late October in Redmond, Washington.