How to hide from taskbar a form showed form mainwindow

[tonnot]

I'm used exec() to show my form in 'modal' way from the main window.

NewForm newform(this);
newform.exec();

NewForm newform(this);
newform.exec();

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But, I see the my main app and the second form names at the task bar.
Logically i'm talking about Windows...
Any idea ?
Thanks