Windows 2000

Windows 2000 (known as Windows NT 5.0 during development) is an NT-based version of Windows released by Microsoft that succeeded Windows NT 4.0. Its Professional SKU was replaced by Windows XP, while its Server SKUs were replaced by Windows Server 2003. Windows 2000 was the last NT-based Windows product before the unification of the Windows NT and DOS-based line. It reached general availability on 17 February 2000 after releasing to manufacturing two months prior on 15 December 1999. Windows 2000 targeted both the high-end consumer market, as well as server and business markets. Multiple SKUs were made for both client and server uses, albeit the user interface remains largely the same. Even though Windows 2000 was intended mainly for use in businesses unlike Windows Me (which was more targeted at home users), many home users ended up buying the Professional SKU of Windows 2000 during the time due to the highly significant issues that plagued Windows Me.

During the course of its support, four Service Packs and an update rollup were released for Windows 2000. Microsoft had originally intended to release a fifth service pack for Windows 2000, but eventually canceled it, and in 2005 instead released the Update Rollup 1 for Windows 2000 Service Pack 4, a collection of all the security-related hotfixes and some other significant issues. The Update Rollup does not include all non-security related hotfixes and is not subjected to the same extensive regression testing as a full-service pack. Microsoft states that this update will meet customers' needs better than a whole new service pack, and will still help Windows 2000 customers secure their PCs, reduce support costs, and support existing computer hardware. Microsoft ceased support for Windows 2000 on 13 July 2010, over ten years since its release.

This is the last version of Windows for the PC-98 series of the x86 architecture, the last version of Windows NT Client to use the Windows Classic theme and the last version of Windows NT to use the classic Start menu as default.

Naming
Prior to the final announcement, Windows 2000 was called Windows NT 5.0 both in marketing materials and the operating system builds themselves. On 27 October 1998, Microsoft announced the renaming of the Windows NT 5.0 product line to Windows 2000, which according to Microsoft reflects the growing mainstream role of Windows NT. The name continues the year-based naming scheme for consumer-oriented versions of Windows, which started with Windows 95. This reflected the initial plan for Windows 2000 to succeed both the consumer-oriented Windows 98 and business-oriented Windows NT 4.0 operating systems. However, in the end, Windows Millennium Edition was released to succeed Windows 98, which led to confusion between the two. Due to the removal of the NT moniker, Windows 2000 branding often included the "Built on NT Technology" tag line to clear out doubts.

An internal Microsoft presentation released during the U.S. v. Microsoft trial titled "Windows Launch Review" from 21 November 1997 briefly discusses naming options of the workstation edition. According to the document, Microsoft considered the following names:


 * Windows NT Workstation 5.0
 * Windows NT Client 5.0
 * Windows NT Desktop 5.0
 * Windows NT 5.0
 * Windows NT Server 5.0
 * Windows 99/2000

Editions
There are 4 major editions of Windows 2000. One of the server editions, Windows Small Business Server 2000, is technically considered a separate version. Files from the IA-64 compile of Windows Server 2003 build 2462 show a "Windows 2000 Personal" login banner, which indicates that such edition could also have been in planning. A version of Windows 2000 Advanced Server, known as Windows Powered, was made for network-attached storages - abbreviated to NAS. Windows Powered is only obtained using a utility created by Microsoft - known as Microsoft Server Appliance Kit - that converts Advanced Server to Powered. An MSDN release was sent out to people who wished to evaluate Powered, but an update was pushed out to revert the branding to the Advanced server branding.


 * Windows 2000 Professional
 * Windows 2000 Server
 * Windows 2000 Advanced Server
 * Windows 2000 Datacenter Server

Source code leak
In early 2004, a portion of the Windows 2000 source code leaked online, together with the source code of Windows NT 4.0. The source of the leak was traced to Mainsoft, the developer of MainWin, a program allowing porting of Windows programs to Unix systems, whose development required access to selected portions of Windows source code under Windows Interface Source Environment program. In response, Microsoft released the following statement: "On Thursday, February 12, Microsoft became aware that portions of the Microsoft Windows 2000 and Windows NT 4.0 source code were illegally made available on the Internet. Subsequent investigation has shown this was not the result of any breach of Microsofts corporate network or internal security, nor is it related to Microsofts Shared Source Initiative or its Government Security Program, which enable our customers and partners, as well as governments, to legally access Microsoft source code. Microsoft reaffirms its support for both the Shared Source Initiative and the Government Security Program.

Microsoft continues to work closely with the U.S. Federal Bureau of Investigation and other law enforcement authorities on this matter. Microsoft source code is both copyrighted and protected as a trade secret. As such, it is illegal to post it, make it available to others, download it or use it. Microsoft will take all appropriate legal actions to protect its intellectual property. These actions include communicating both directly and indirectly with those who possess or seek to possess, post, download or share the illegally disclosed source code.

Specifically, Microsoft is sending letters explaining to individuals who have already downloaded the source code that such actions are in violation of the law. Additionally, Microsoft has instituted the use of alerts on several peer-to-peer clients where such illegal sharing of the source code has taken place. These alerts are designed to inform any user who conducts specific searches on these networks to locate and download the source code that such activity is illegal.

Questions about the ongoing investigation should be referred to the FBI."

- Microsoft Corporation Despite the warnings, the archive containing the leaked code spread widely on the file-sharing networks and, even later, on open-source repository websites. On 16 February 2004, an exploit allegedly discovered by an individual studying the leaked source code for certain versions of Microsoft Internet Explorer was reported. On 15 April 2015, a repository containing the leaked NT 4.0 source code was removed from GitHub at Microsoft's request, although other repositories hosting the Windows 2000 source code continued to exist in the same website; most of them were taken down by Microsoft's request on 9 April 2021.