A war is brewing between Microsoft and Gears of War creator Epic Games, once strong allies in the business of making video games, and the battlefield is your Windows computer.

This morning, Epic Games co-founder Tim Sweeney penned an opinion piece that ran in the U.K. newspaper The Guardian. In it, he accuses Microsoft of trying to use a new program standard built into Windows 10 to turn the operating system into a monopolistic walled garden with the help of the Windows Store.

He writes that the relatively new Universal Windows Platform, which allows developers to create a single program that can run on a variety of Windows devices — from tablets and phones to computers and virtual reality headsets — is in essence a "closed platform-within-a-platform."

We've reached out to Microsoft for comment and will update this story when they respond.

The Guardian open letter, Sweeney told Polygon in a follow-up interview, came after months of secret talks between Sweeney and highly placed executives at Microsoft, including Xbox head Phil Spencer. Sweeney said the company was always willing to listen, but never acted on his concerns. He decided to write the letter, he said, because he sees Microsoft ramping up its efforts to market the Windows Store more aggressively.

"Very recently, in this last week, they launched a bunch of games on Windows Store and had a major marketing event around it, promoting the store and the integration of the Xbox Live service with Windows available through [the Universal Windows Platform] and putatively only through UWP," Sweeney said. "This indicates they're starting to now give UWP programs advantages over regular Windows programs and drive people more and more into this ecosystem.

Now is the time

"So now is the time."

While Sweeney said he is greatly concerned about some of the implications of the current policies surrounding UWP, he does believe that UWP applications should eventually replace the current standard, which is easily misused to inject viruses and other malware into computers. His issue, he said, isn't with UWP, but rather the way Microsoft is using it.

"I see there could be a bright future ahead [for UWP] if Microsoft could just stop this silly thing," he said.

Any program created with UWP essentially has to be installed through the Windows Store. (Enabling a UWP app to be installed without the store requires making technical changes in a computer's buried registry.) That requirement, Sweeney argues, gives the Windows Store an unfair marketplace advantage.

Using the store means agreeing to pay Microsoft 30 percent of sales, and also gives the company the ability to be the gatekeeper for content — something Microsoft could use to, for instance, block competing online marketplaces from being installed on Windows.

Sweeney told Polygon that his bigger concern is that by pushing developers into using the Windows Store and enticing customers to use the store by tying new features on Windows 10 to the marketplace, the store will eventually become the standard.

There is not proof of an evil plan to do this, but just the fear

"That's my concern," he said. "Microsoft is a black box. I know a lot of people there who are really awesome, smart people who want to do the right thing, but then there are other people there who appear not to be because [of] some of the bad decisions they're making on Windows 10. There is not proof of an evil plan to do this, but just the fear.

"We want to fight for our rights as independent software developers to make PC software without Microsoft's permission. My tendency is to fight this really early on as they're starting to do this."

If and when UWP were to become a standard, he said, Microsoft could stop supporting the current Win32 standard and essentially cut competing online stores like GOG, Origin, Battle.net, Steam and Epic's own game launcher completely out of the picture.

"There is a story that ... if you try to throw a frog into boiling water it will jump right out, but if you put a frog into cold water and then slowly turn the temperature up, you can boil him, and it will never notice that the temperature of the water got too hot," Sweeney said. "The hope here is that we avoid boiling the frog by starting to think about this problem and deal with the problem very early on before it becomes so pervasive that Microsoft with its hundreds of billions of dollars of market value can't just steamroll everybody."

Make sure you listen to the full interview on our Newsworthy podcast, embedded below, to hear where Sweeney's concerns stem from, why he sees it as something that could have an impact on things beyond games, and how he believes the problem can be fixed. There's a lot of nuance in his argument, and it's hard to summarize aptly.