Windows Longhorn build 4050 (private/lab06 demo.031022-1934)

Windows Longhorn build 4050 (private/lab06_demo.031022-1934) is a private build of Windows Longhorn. This build was shown during the PDC 2003 conference and is known to have Aurora and Aero transparency. During the demonstration, Hillel Cooperman showed the new Aero transparency, which more than 40 people worked on for over a month, and also opened a MS-DOS application to prove that this was not a concept but a real build. A copyright notice at the bottom left of this build can be seen, stating the following: "©, TM Microsoft Corp. All rights reserved. User interface is ™ and trade dress of Microsoft Corp." On 27 September 2018, ReflectiaX claimed to have a copy of this build on the BetaArchive forum.