Window Hider

Window Hider is a tiny utility that enables you to hide the windows of any opened program using password protection. It can help you prevent other people from snooping around your work when you're away from the computer.

No setup necessary, besides .NET Framework

The entire tool's wrapped in a single .exe file that you can copy to the hard drive or to a USB flash disk to directly launch it on any computer. However, you must have .NET Framework installed, since it was developed with the aid of this platform. It doesn't create other files on the HDD without your permission and doesn't modify Windows registry settings.
Once started, Window Hider creates an icon in the taskbar notifications area and sits there silently. This way, it becomes non-intrusive and lets you carry on with your normal PC activity without any interruptions.

Hide windows from the systray

In order to hide the window of an active application, all you have to do is select its entry from the tray icon's right-click menu. Specifying a password to hide and make the tool visible again is optional. Worth noting is that distinct or identical keys may be assigned to multiple programs, depending on how many passwords you're willing to memorize.
Once hidden, the app in question can only be seen in the Task Manager. Although it's necessary to enter the right password to unlock it, the workaround is to terminate its process from the Task Manager to restart it, in case you have forgotten the key. Evidently, this means that any unsaved work will be lost.

Evaluation and conclusion

Unsurprisingly, it used a low amount of CPU and RAM in our tests. No stability issues occurred and Window Hider didn't freeze or crash. Thanks to its straightforward approach, it can be used by anyone who wants to hide windows via password protection.