It is more common in U.S. airports because you are not required to be a departing passenger to pass through airport security. In Canada you are required to have a boarding pass. There will be at least two people involved, the first of whom passes through with no problems. As this person delays your passage through to the other side, the accomplice, the first person to pass through security, takes your notebook and disappears.
Scam artists wander airports until they spot a traveler with a portable.
When placing your portable on the X-ray conveyor ensure the operators recognize it is yours and that you will be picking it up on the opposite side. All products mentioned are trademarks or registered trademarks of their respective corporations.