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Paolo Iannelli

Big Daddy at Mega Labs

Amsterdam Area, Netherlands
Information Technology and Services
C, Python, Big Data, Scalability, High Availability, Performance
Expert Software Engineer with more than 12 years of experience.
Strong in critical thinking, problem solving and high performance architectures.
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Most annoying Windows 7 bug : trick your friends!

Posted on : 23-03-2011 | By : Paolo Iannelli | In : Security, System Administration

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It is now at least two years that I discovered this bug, but still Microsoft probably didn’t even identify it.

I tried it with Windows 7 Enterprise Edition and Ultimate edition, but other versions might be affected as well.

The bug is pretty annoying when you have people around and you lock the workstation.

In fact, anyone can enable the High Contrast for accessibility on your machine, even without unlocking your workstation !

The result is that when you log back in, apparently everything is normal, but your color scheme suddenly get switched to High Contrast.

Imagine how this can piss you off if you don’t know it!

There is only one requirement : the machine must be locked (so the user should have been logged already in and locked the workstation after)

How do I do that ?

It is pretty easy.

When your victim’s machine is locked, go to Accessibility options in the bottom right and enable the High Contrast feature, then press OK.
Now click on Switch User : you will be redirected back to the user selection screen (Windows may ask to press CTRL+ALT+DEL for it) with normal contrast settings.
Proceed clicking on the user that was logged in and leave the screen with the password field as it is.

When the victim will type his password, he will resume his session, but with a “WTF?!?“, because his color scheme will be switched on High Contrast !


I don’t assume any responsibility if any of your colleagues or friends will kick you for doing this !

Have fun and I hope Microsoft will now fix this bug in one of their software updates !

P.S. : if you get any video of your friends getting crazy with it, place a link to the video in a comment =)