Microsoft appears to be testing a new type of ad inside File Explorer on Windows 11. Microsoft MVP and Twitter user Florian Beaubois discovered an ad in the latest test build of Windows 11, prompting users to check out the Microsoft Editor. While the ads might have appeared for some Windows 11 users, Microsoft says it was a mistake.

“This was an experimental banner that was not intended to be published externally and was turned off,” says Brandon LeBlanc, senior program manager for Windows, in a statement to The Verge.

While the ads weren’t intended to be tested externally, it’s clear Microsoft is capable of running them inside Windows 11, and the company’s brief statement doesn’t rule out ads appearing in the File Explorer in the future.

This isn’t the first time Microsoft has placed ads inside File Explorer, either. The software maker added a large banner ad to the Windows 10 File Explorer in 2017, promoting subscription options for its OneDrive cloud storage service. While the ads can be easily dismissed, they’re still a frustrating experience in an operating system that’s traditionally been ad-free.

Microsoft has been experimenting with ads inside Windows for a decade now. It already places ads on the Windows 10 lock screen and in the Start menu, and there have been plenty instances of annoying pop-up ads in the taskbar, too. Lots of Windows 8’s built-in apps also had ads inside them.

Sadly, Microsoft isn’t alone in advertising its own services in its operating system or apps. Apple spams you with offers for Apple Music, Apple Fitness, and iCloud if you buy a new iPhone, and we’ve even seen full-screen ads for Apple TV Plus if you own Apple’s TV hardware. Google will hound you with pop-up ads until you give in and buy a YouTube Premium subscription.