Question

Many questions on SO say “Windows developer guidelines” or “windows design guidelines” say that you shouldn’t write temporary or program data to the Program Files area, but as far as I can tell none of them actually link to a piece of documentation that says as much. Searching the MSDN has yielded me no results. Windows will make the area read-only, so it can be enforced by the OS, but that doesn’t mean developers didn’t try to write there anyway (e.g., when porting older, XP and earlier based programs forward.)

I realize that it seems odd to ask about it this late into Windows development (since, as a commenter below pointed out, has been enforced by the OS for more than a decade), but a document that says so is sometimes necessary to satisfy people.

With that in mind, Does Microsoft have a document published stating we shouldn’t write application data to the Program Files area, and if so, where is it?

Answer 1

From Technical requirements for the Windows 7 Client Software Logo Program:

Install to the correct folders by default

Users should have a consistent and secure experience with the default
installation location of files, while maintaining the option to
install an application to the location they choose. It is also
necessary to store application data in the correct location to allow
several people to use the same computer without corrupting or
overwriting each other’s data and settings.

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Windows provides specific locations in the file system to store
programs and software components, shared application data, and
application data specific to a user:

• Applications should be installed to the Program Files folder by default. User data or application data must never be stored in this
  location because of the security permissions configured for this
  folder (emphasis added)
• All application data that must be shared among users on the computer should be stored within ProgramData
• All application data exclusive to a specific user and not to be shared with other users of the computer must be stored in
  Users\<username>\AppData
• Never write directly to the “Windows” directory and or subdirectories. Use the correct methods for installing files, such as
  fonts or drivers
• In “per-machine” installations, user data must be written at first run and not during the installation. This is because there is no
  correct user location to store data at time of installation. Attempts
  by an application to modify default association behaviors at a machine
  level after installation will be unsuccessful. Instead, defaults must
  be claimed on a per-user level, which prevents multiple users from
  overwriting each other’s defaults.

And I’m quite sure that there’s similar stuff for every Windows version of the NT family going back to Windows NT 4 or even earlier.

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See also this question.

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Edit: the original link in this post to the Windows 7 Logo program exists no more. Here you find the current link to the Certification requirements for Windows Desktop Apps. See Section 10, Apps must install to the correct folders by default