No close window
In both Internet Explorer and Netscape it is possible to create a browser window that can't be closed. This unclosable window effectively crashes a system because no other windows can be accessed on the screen.

The unclosable window works by taking over the "blur" and "unload" events. If there is attempt to switch away from the window, a "blur" event will be generated. The blur event handler (function "myfocus") cancels the blur event by issuing its own focus event. The result is that the unclosable window always stays on top.

To prevent the window from being closed, the page also installs an unload event handler (function "myreload"). When a unload event occurs, this handler loads a second copy of the page effectively making it impossible to kill the window. Even attempting to kill the window with an "End Task" command after pressing CTRL-ALT-DEL doesn't seem to work.

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by http://www.computerbytesman.com
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