But users say the tool is simply returning a blank box. As many as 800million people use Windows 10 around the world, but it's not clear how many people are affected by today's bug.

"I erased my drive when I set up a Dual 2.7GHz G5 tower for sale, and installed Leopard. Updated to 10.5.4. Then found that when I open System Preferences, I get a blank white window.