TUAW late last week reported on a customer who purchased a new 27-inch iMac earlier in the week and allegedly received a prerelease version of Mac OS X 10.6.3 via Software Update. Mac OS X 10.6.3 has not yet been released to the public, with the latest version being seeded to developers just this past Friday. That version, Build 10D572, is the same as the one somehow received automatically by the iMac customer.
This kind of update does not normally appear in the wild on Software Update. Prerelease, and specifically "**PRERELEASE**", updates refer to Apple-internal builds distributed to any Apple employee who has access to Apple's VPN. A **PRERELEASE** build is typically seeded to employees 24 to 48 hours before the build goes public via Software Update.
It is unclear how a brand-new retail machine would automatically have access to Apple internal builds, and there have been no other public reports of such access at this time. Consequently, it is difficult to assess the veracity of the claim, although it would add to the growing evidence of an imminent Mac OS X 10.6.3 public release if true.