Metro apps for Windows 8 will be available only through Microsoft's own store, the company said at its BUILD Windows conference last week.

But although Microsoft went to pains to say that it would not discuss the business end of the app store -- including what percentage the company will return to developers -- a primer of the download market published by Microsoft said that it, like Apple, will take a 30% cut of all sales.

Last week, Microsoft confirmed that the Windows Store -- the official name for what executives have referred to as "our Windows app store" -- will be the sole distribution channel for Metro apps, those that run in the Metro interface in Windows 8 on Intel-powered devices, and the only ones that will be permitted on ARM-based Windows 8 tablets.

Microsoft is restricting Metro app distribution to ensure the software is secure and appropriate, said Ted Dworkin, a Microsoft director who leads the Windows Store development team, in a BUILD session Wednesday.

"We will be the only store for distribution of Metro-style apps," said Dworkin.

That means Microsoft will follow Apple's model, not Google's. The former limits distribution of iOS apps to the App Store; although Google operates the Android Market, apps can be acquired elsewhere.

Dworkin also told developers that Microsoft will vet each submission and ensure that Metro apps are malware-free. "We will examine every application that will be submitted to us [and] we will run a virus check and a malware check on every application," Dworkin said.

Those scans also separate Microsoft's upcoming store from Google's Android Market, which this year has had to yank dozens of apps that contained attack code.

But even as Dworkin talked up the Windows Store, he declined to disclose Microsoft's business model. "We are not going to spend time [today] on the specific store policies and the specific business terms," said Dworkin on Wednesday. "We will describe them in great concrete detail [later]. At the point when we're ready for [app] submission, that's the point at which you will understand what the specific store policies and business terms are."

However, Microsoft did briefly reveal information about the business model in an online document.

"Following industry norms, developers pay a nominal yearly fee to upload apps to the Store, and receive 70% of the gross income from those apps (for paid apps and in-app purchases that use the default commerce engine)," said the "Primer for current Windows developers."

That primer, which was first noted by Windows blogger Long Zheng on his istartedsomething website, was quickly revised to strip out the references to revenue sharing.

A cached version of the primer available on Thursday -- but since deleted -- confirmed the 70-30 split between developers and Microsoft.

If Microsoft follows through on the revenue sharing -- the primer said, "This documentation is preliminary and is subject to change" -- the Windows Store would mimic not only the business model of Apple's App Store, but also that of its own Windows Phone 7 e-store.

Another since-scoured part of the primer told Metro developers that they must give customers a five-device license for any purchased app. "Any customer who pays for an app can install and use that app on up to 5 Windows Developer Preview devices, so that the app can engage that customer across a range of form factors," said the documentation.

The end-user license of Apple's App Store and Mac App Store lets users install and use a purchased program on all their personally-owned or controlled devices.

The Microsoft Store will also offer non-Metro applications -- a key difference from Apple, which splits apps into two download marts -- executives said earlier in the week.

Desktop applications in the app store will get a free ride, said Antoine LeBlond, the vice president of Microsoft's Web services group, during a BUILD keynote. "We're giving these Win32 apps a free listing service and exposing them to all of the hundreds of millions of Windows users," said LeBlond, who noted that x86 apps would not have to toe the five-license line required of Metro programs.

Microsoft has not said when it will ship Windows 8, or when it will launch the new Windows Store with Metro apps.

Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer, on Google+ or subscribe to Gregg's RSS feed . His e-mail address is gkeizer@computerworld.com.

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