The Halloween documents comprise a series of confidential Microsoft memoranda on potential strategies relating to free software, open-source software, and to Linux in particular, and a series of media responses to these memoranda. Both the leaked documents and the responses were published by Eric S. Raymond in 1998.
The documents are associated with Halloween because many of them were originally leaked close to the 31st of October in different years.
The first Halloween document, requested by senior vice-president James Allchin for the attention of senior vice-president Paul Maritz and written by Microsoft program manager Vinod Valloppillil, was leaked to Eric Raymond in October 1998, who immediately published an annotated version on his web site. The document contained references to a second memorandum specifically dealing with Linux, and that document, authored by Vinod Valloppillil and Josh Cohen at Microsoft, was also obtained, annotated and published by Raymond. Microsoft has since acknowledged the documents' authenticity.
Marked "Microsoft confidential", they identified open-source software, and in particular the Linux operating system, as a major threat to Microsoft's dominance of the software industry, and suggested ways in which Microsoft could disrupt the progress of open-source software.
These documents acknowledged that free software products such as Linux were technologically competitive with some of Microsoft's products,  and set out a strategy to combat them. These views contradicted Microsoft's public pronouncements on the subject.
Since the publication of the two original documents, a number of additional Microsoft memoranda on related topics have also been leaked and published (e.g. Halloween VII).
List of documents
The documents are from a variety of sources. Only some are leaked internal memos (documents I, II, VII, VIII, and X). One is a public statement (document III). The others are responses by Eric Raymond to various columns, news articles, and other works.
|I||Open Source Software: A (New?) Development Methodology||Vinod Valloppillil||August 1998||A leaked internal report|
|II||Linux OS Competitive Analysis: The Next Java VM?||Vinod Valloppillil||August 1998||A leaked internal report|
|III||Untitled statement||Aurelia van den Berg||November 1998||Press statement from Microsoft Netherlands|
|IV||When Software Things Were Rotten||Eric S. Raymond||December 1998||A satire piece based on Microsoft's Ed Muth comparing open source developers to Robin Hood.|
|V||The FUD Begins||Eric S. Raymond||March 1999||A response by Raymond to Ed Muth's allegations that Linux has a "weak value proposition".|
|VI||The Fatal Anniversary||Eric S. Raymond||October 1999||A response by Raymond to studies authored by the Gartner group for Microsoft.|
|VII||Research E-Bulletin: Attitudes Towards Shared Source and Open Source Research Study||September 2002||A summary of the results of a Microsoft survey describing reactions to Microsoft's shared source program.|
|VIII||OSS and Government||Orlando Ayala||November 2002||Describes Microsoft's procedures for responding to notable conversions away from Microsoft software|
|IX||It Ain't Necessarily SCO||Rob Landley and Eric S. Raymond||August 2003||A response to the allegations made by the SCO Group in its initial filings in SCO v. IBM.|
|X||Follow The Money||Mike Anderer||March 2004||An e-mail from consultant Mike Anderer to SCO's Chris Sontag revealing Microsoft's channeling of US$86 (equivalent to $107.74 in 2015) million to SCO.|
|XI||Get The FUD||Eric S. Raymond||June 2004||A response to Microsoft's Get the Facts campaign|
Documents I and II
These are leaked reports for Microsoft's own use, both written by Vinod Valloppillil, who was a Program Manager at Microsoft.
Document I provides a detailed introduction to the concepts behind Open Source software and its possible impact on Microsoft products and services. It outlines the strengths and weaknesses of Open Source software. Document II describes the basic architecture of the Linux system, its relation to Unix and Windows NT.
Document I revealed that "FUD" (spreading fear, uncertainty, and doubt) was a traditional Microsoft marketing strategy, acknowledged and understood internally. Examples of Microsoft's FUD tactics are announcing nonexistent products or spreading rumors that competing products will crash Windows.
Raymond suggests that the documents show that while Microsoft may be dismissive of open source software in public, it considers it a serious competitor in private.
While discussing ways of competing with open source, Document I suggests that one reason that open source projects have been able to enter the market for servers is the use of standardized protocols. It then suggests that this can be stopped by "extending these protocols and developing new protocols" and "de-commoditize protocols & applications." This policy has been nicknamed "embrace, extend, extinguish".
Document I also suggests that open source software "is long-term credible ... FUD tactics can not be used to combat it," and "Recent case studies (the Internet) provide very dramatic evidence ... that commercial quality can be achieved / exceeded by OSS projects."
The statement from Aurelia van den Berg, the Press and Public Relations manager of Microsoft Netherlands, puts forward Microsoft's view on the first two documents. It says that the documents are not an "official position", but that "it is routine and appropriate" to research competitors.
This statement is only a brief response, but many points were later incorporated into an official response from Microsoft.
This document is a summary of the results of a survey of developers and IT managers, carried out by Microsoft, describing reactions to Microsoft's shared-source program. Eric Raymond provides commentary suggesting ways that the open-source community can promote itself based on the results of the survey.
The results show favorable responses about both open-source and shared-source principles. It also describes low total cost of ownership as a major reason for Linux adoption, in contradiction to many documents released by the company suggesting that Windows has a lower TCO than Linux solutions. 
"OSS and Government", aka Halloween VIII: Doing the Damage-Control Dance. A memo from Group Vice President of Worldwide Sales, Orlando Ayala, to general managers of Microsoft regional subsidiaries. Describes the availability of support from Microsoft corporate for regional sales personnel facing competition from Linux in government markets.
An e-mail from consultant Mike Anderer to SCO Group's Chris Sontag, also known as Halloween X: Follow The Money. The document describes, among other points, Microsoft's channeling of US$86 (equivalent to $107.74 in 2015) million to SCO.
- Harmon, Amy (November 3, 1998). "Internal Memo Shows Microsoft Executives' Concern Over Free Software". The New York Times. Retrieved 2011-11-05.
- "Microsoft Responds to the Open Source Memo Regarding the Open Source Model and Linux". Windows NT Server 4.0 website. Microsoft. November 5, 1998. Archived from the original on October 13, 1999. Retrieved June 2, 2012.
- "Halloween Document 10". www.catb.org. Retrieved 2016-02-22.
- "Halloween Document 10". www.catb.org. Retrieved 2016-02-22.
- Rosenberg, Scott (November 4, 1998). "Let's Get This Straight: Microsoft's Halloween scare". Salon. Salon Media Group. Retrieved June 2, 2012.
- "Plaintiff's Exhibit 6501" (PDF). Exhibits Offered by Plaintiffs on 1.11.07 and Admitted by the Court on 1.16.07. iowa.gotthefacts.org. January 16, 2007. Archived from the original (PDF) on November 7, 2007. Retrieved June 2, 2012.
- "Get the Facts: Total Cost of Ownership". Microsoft.
- "Windows 2000 Versus Linux in Enterprise Computing" (PDF). IDC.
- "Study Finds Windows Cheaper Than Linux". eweek.com.
- Rodger, Will (November 9, 1998). "Intel exec: MS wanted to 'extend, embrace and extinguish' competition". ZDNet. Washington: CBS Interactive. Retrieved June 2, 2012.
- Jones, Pamela (January 8, 2007). "Expert Testimony of Ronald Alepin in Comes v. Microsoft - Embrace, Extend, Extinguish - Updated". Groklaw. Retrieved June 2, 2012.
- Erickson, Jonathan (August 1, 2000). "Embrace, Extend, Extinguish: Three Strikes And You're Out". Dr. Dobb's Journal. UBM. Retrieved June 2, 2012.