Microsoft cracked down Wednesday on several Web sites that had posted screenshots of the most recent build of its next-generation Windows operating system, Longhorn, telling them that they were violating the beta licensing agreements.

Enthusiast Web site Neowin pulled the images when Microsoft said that posting them violated the EULA (End User License Agreement) of the preview edition distributed at the conference. The site had obtained the images at Microsoft's Windows Hardware Engineering Conference that wrapped Wednesday in Seattle.

Some sites, such as Paul Thurrott's SuperSite for Windows, initially refused to comply, but eventually bowed to Microsoft when told that patents for certain technologies in the preview had not yet been filed, including the user interface, and publishing the screenshots risked copycats.

But the move fueled an ongoing controversy among bloggers and Windows enthusiasts that Microsoft was embarrassed at the appearance of the current UI for Longhorn. And at least one long-time Windows supporter chided Microsoft. "Way to throttle back the enthusiasm even further, guys," wrote Paul Thurrott on his Web site.