The Halloween documents are a series of confidential Microsoft memoranda on its strategies related to Open source software and on Linux in particular. The first Halloween document, written by Microsoft engineer Vinod Valloppillil, was leaked to Eric S. 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 admitted the documents' authenticity.

Marked "Microsoft confidential", they identify open source software (OSS), and in particular the Linux operating system as a major threat to Microsoft's dominance of the software industry, and suggest ways in which Microsoft could disrupt the progress of open source software.

These documents acknowledged the technical superiority of Open Source/Free Software/Linux to some of Microsoft's products, and set out a strategy to combat them. The documents were embarrassing largely because they 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. Together, these documents demonstrate Microsoft's continued awareness that its open-source competitors are a potential threat to its livelihood in the software industry.

Quotes from the Halloween documents:

  • "Recent case studies (the Internet) provide very dramatic evidence ... that commercial quality can be achieved / exceeded by OSS projects."
  • (Open source software) "is long-term credible ... FUD tactics can not be used to combat it."
  • "Linux can win as long as services / protocols are commodities."
  • (Microsoft should) "De-commoditize protocols & applications"

The last strategy has been described by others as "Embrace, extend and extinguish".

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