In new regulatory filings, Microsoft has eliminated Linux as an existential threat to the company’s Windows empire, and elevated Apple and Google to the position of being its “main” competitors. The change in perspective occurred in Microsoft’s 2011 10-K filing with the Securities & Exchange Commission (SEC), a document that includes a list of competitive threats that it feels investors should know about.

For most large corporations, this list is often comprised of a mix of boogeymen and true competitors, all of which form a sort of CYA protection just in case of adverse results in the future.

For instance, Apple’s own 10-K filing from 2010, the company states, “The Company is confronted by aggressive competition in all areas of its business,” adding, “The principal competitive factors include price, product features, relative price/performance, product quality and reliability, design innovation, availability of software and peripherals, marketing and distribution capability, service and support, and corporate reputation.”

How much of that is really true? Not much, but it’s the sort of thing that responsible companies (and their corporate officers and lawyers) are required by the SEC to identify so that investors can better understand what they might be getting themselves into, should they bother to look.

For some time, Microsoft has listed Linux as one of its cheap competitors. Microsoft may have seen the free, open source operating system as more than a boogeyman, too. As recently as 2001, the company spent a considerable amount of effort to smear open source licensing as un-American, and to label the General Public License (GPL) as a destroyer of Intellectual Property.

Good times, for sure.

In fiscal 2010, Microsoft said that its consumer Windows empire faced, “competition from various commercial software products by well-established companies, including Apple and Google and the Linux operating system.” The company went on to detail that Linux was free and open source and super bad.

Writing for ZDNet, Ed Bott noted that the company’s new 10-K filing for fiscal 2011 has completely ommitted the mention of Linux as a competitive threat to Windows, and elevated Apple and Google from being mere examples of competition to being the company’s main rivals.

From the new 10-K:

The Windows operating system faces competition from various commercial software products offered by well-established companies, mainly Apple and Google.

No longer is Linux, open source software, or the GPL license used by the open source movement even mentioned as competition, at least not on the consumer side. Microsoft does continue to mention “Linux” and “Unix” as significant competitors to its server and Enterprise business, markets where Linux has a considerable foothold.

This truly does represent a seismic shift in Microsoft’s stated priorities. Discounting Linux as a threat to Windows and specifically elevating both Apple and Google (and note the order of those names) as the company’s main competitors is a sign that Microsoft is likely going to be more aggressive in defending its territory (in the case of Windows) and trying to gain new territory (in the case of search and mobile) in the future.

From more Microsoft retail stores with choreographed dancing to the company partnering with Nokia to deliver Windows Phone 7 devices to working to get Bing onto as many mobile apps as possible, it’s Apple, the Mac, and iOS, as well as Google and its Android platform, that are now in Microsoft’s sights.