Since we silently opened Windows Marketplace for Mobile to developers for registration two weeks ago (and it’s still not open to folks outside of the US or the UK, sorry for that, we are working on it), there have been some rumours (here and here and here and here and here, e.g.) about a “secret” list of “illegal” application types that Microsoft tries to exclude from Marketplace, and is has been speculated a lot about the (mostly inferior) motives behind this decision.

While we have to admit that the discoverability of the list needs some improvement (it’s not clearly pointed to from the main Marketplace or the signup pages, afaik), it is by no means secret, and it is available now publicly – just follow this link to the PDF document.

Here is this list of applications that can’t be distributed via Marketplace:

1. Applications that are or distribute alternate marketplaces for content types (applications, games, themes etc.) that are sold or otherwise distributed through Windows® Marketplace for Mobile.
2. Applications that link to, incent users to download, or otherwise promote alternate marketplaces for content types that are sold or otherwise distributed through Windows Marketplace for Mobile.
3. Applications that promote or link users to a website, or contain functionality within the application itself, which encourages or requires the user to purchase or pay to upgrade the application outside of Windows® Marketplace for Mobile.
4. Applications that enable VoIP (Voice over IP) services over a mobile operator network.
5. Applications that sell, link to, or otherwise promote mobile voice plans.
6. Applications that display advertising that does not meet the Microsoft Advertising Creative Acceptance Policy Guide http://advertising.microsoft.com/creative-specs.
7. Applications that replace, remove or modify the default dialer, SMS, or MMS interface.
8. Applications that change the default browser, search client, or media player on the device.
9. Applications with an OTA (over the air) installation file larger than 10MB.
10. Applications that run code outside Microsoft runtimes (native, managed, and widgets).
11. Applications that publish a user’s location information to any other person without first having received the user’s express permission (opt-in) to do so, and that do not provide the user a means of opting out of having their location information published.
12. Applications that publish a user’s data from their mobile device to any other person without first having received the user’s express permission (opt-in) to do so, and that do not provide the user a means of opting out of having their data published. A “user’s data” includes, without limit, contacts, photos, SMS or other text communication, browsing history, location information, and other data either stored on the mobile device or stored in the “cloud” but accessible from the mobile device.

I believe it is very clear why we impose these restrictions: to make sure Windows Mobile users have a smooth and reliable user experience with Marketplace, with as little confusion or issues about the shopping experience as possible (1, 2, 3, 9), to play by the rules of the mobile operators (4, 5), to protect the functionality of the user’s phone (7, 8), for security reasons (10), to protect against overly aggressive or annoying advertising (6), and to protect the user’s privacy (11, 12). These rules are commonplace today in application stores like this. If you, as a developer, do not like these rules, or if your application cannot be made compatible with these rules (because it is larger than 10 MB, e.g.), then you can continue to use the same distribution mechanisms that have been used up to now. (Your website, 3rd party application stores, etc.) You have the freedom of choice here! (Unlike on some other popular mobile platform where you have to play by the rules of the platform/device manufacturer, or you are excluded. Think about it.) Marketplace gives your software more visibility and discoverability on the devices, but if you want this, you have to follow some rules. There is no free lunch.

If you have any questions or comments on this, feel free to ping me.