Internet Explorer 10 in Windows 8 will include a bundled, integrated version of Adobe Flash, and the Metro-style browser will support the use of Flash on a limited number of sites. This news and corroborating screenshots come from Within Windows and winunleaked.tk.

In Windows 8, Microsoft's browser will come in two guises. There will be the traditional desktop browser, with its full support of plugins and extensions, and there will be the new Metro-style browser that will be plugin free. But that's not quite the whole story. The browser will include an integrated and embedded version of Adobe Flash, and because this will be built in, it won't be treated as a plugin.

The result? Even the Metro-style browser will be able to use Flash.

Microsoft isn't opening the floodgates entirely. Use of Flash in the Metro-style browser will be limited to those sites included on a whitelist. The list is comprised of a mix of domains: video sites such as Hulu, YouTube, and Vimeo; news sites including CNN, the BBC, and Wired; and a number of entertainment and gaming sites, including Facebook and Zynga. Flash-based interactive content on these sites will work in the Metro-style browser. Flash content on other sites will require the use of the desktop browser.

The move is a little surprising, given Microsoft's oft-repeated commitment to the plugin-free, standards-based Web. Our sources tell us that it was motivated by two things. First, a certain degree of pragmatism. The use of Flash to deliver video, especially video subject to DRM restrictions or with embedded advertising, remains abundant. The same is true of highly interactive content and games: HTML5 is making inroads into this area, but for the time being, Flash is still dominant.

As such, a full-featured Web experience still demands the use of Flash. The future might be HTML5, but the present is not. Including Flash, in a limited way, provides a path towards that future.

Second, Adobe was apparently extremely keen not to be cut off from the Metro browser. The company may be embracing HTML5, but Flash is a going concern, and will remain so for the next 5-10 years. Flash is still a highly productive tool for the creation of rich, interactive Web content, and Adobe wants to keep it usable, at least until it has the development tools to allow a full migration to HTML5. If the company is to make this transition in an orderly manner, it needs Flash to be usable on Windows 8.

Adobe has adopted Microsoft's Secure Development Lifecycle for its own development, and shared the Flash source code with Microsoft. Adobe has a similar arrangement with Google, which, like Internet Explorer 10, also includes an embedded version of Flash. Microsoft has worked to improve Adobe's code to ensure that it meets the security and power consumption goals it has for Windows 8; the company has also worked on optimizing Flash's usability on touch systems. Security updates for the embedded Flash will be distributed by Microsoft as Internet Explorer patches, again mimicking Google's approach.

The Windows 8 Release Preview, due in early June, will include the Flash plugin.

Our sources believe that the ARM-only Windows RT will also include Flash support, and this would certainly be consistent with Microsoft's desire to enable the transition to an HTML5 future. Adobe abandoned the development of the mobile Flash player used on Android last year. Flash under Windows RT would, however, be the fully fledged Windows Flash player that remains under active development.

Of course, Flash isn't the only plugin technology that is used to provide streaming video and rich interactivity. Microsoft's own Silverlight is used for much the same thing, and this raises an obvious question: will Microsoft create an integrated version of Silverlight just as it's done with Flash? We haven't heard that it will, but it can't be ruled out: one of the sites on the Flash whitelist is Netflix, and that's interesting, because Netflix doesn't actually use Flash for its streaming media. It uses Silverlight.