Microsoft have just finished distributing an internal Beta 1 escrow build to internal beta testers. "Atlanta" is the code-name for Microsoft's rehashed GIANT Software Anti-Spyware. In a memo internally, the company looks clear to distribute the software this coming Thursday calling it "new, it's fresh, and it's all good".
Encouraging employees to install the Beta is one of the many ways Microsoft tests Beta products internally. It's not clear whether the release this Thursday will be a public beta or a private external beta.