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In computing, focus stealing is a mode error produced when a program not in focus (e.g. minimized or operating in background) places a window in the foreground and redirects all keyboard input to that window. This is considered to be an annoyance or hazard to some users because the program may steal the focus while their attention is not on the computer screen, such as when typing while reading copy to the side. This will cause everything typed after the window appeared to be lost - or worse, the typed input may cause an unintended effect in the newly focused window. On slow computers, users are sometimes not even alerted to this behavior in time, because the associated window is only actually displayed several seconds after the actual focus change happened.
Focus stealing can cause damage, as users may, while typing when their attention is away from the screen, inadvertently agree to a program doing something that causes damage. For example, when Microsoft Windows pops up the Disk Cleanup wizard, the user may "agree" to deleting files without realizing that the wizard was waiting for input. Focus stealing can also occasion security breaches, for example, when a user enters a password and the typed password appears instead in a new instant-messaging window in an unmasked input field.
Alternatives to focus stealing
There are a number of alternative methods for grabbing the attention of the user that can be used instead of focus stealing:
- Pulse the application's icon in the task bar, leaving the application in the background
- Output a message to the notification area
- Pulsate the display over scan area
- Use an audible alerting framework
X Window Managers
The following window manager systems allow focus stealing:
- 9wm - fails the launch test[clarification needed], giving focus to window placement facility
- IceWM - fails the launch test, giving focus to newly started applications
- oroboros - fails the launch test, giving focus to newly started applications
Microsoft Windows-based systems use pop-up dialogue boxes which can steal focus from the current application. On versions of Microsoft Windows prior to Windows 7, there is a user setting that will by default prevent a cooperative application from stealing focus when launching another program or popping up a new window or dialogue box. This same method does not work in Windows 7 or later.
Apple MacOS X systems also switch applications from background to foreground when the background applications uses pop-up modal dialogs. Example of this behavior is Google Chrome using alert dialog, as documented in 
Focus-stealing detection programs
Programs have been written to identify what is stealing focus.
- Documentation released by Mark Hobley via the computer accessibility wiki
- "ForegroundLockTimeout". Microsoft TechNet. Microsoft Corporation. Retrieved 18 November 2015.
- "Preventing applications from stealing focus". superuser.com. Stack Exchange Inc. Retrieved 18 November 2015.
- "Tabs can steal focus using alert/prompt/confirm popups". bugs.chromium.org. Retrieved 25 April 2016.
- Mozilla Focus Stealing bugs