Another scam

Our daughter is in the US on business and had an email yesterday telling her that her flight had been cancelled. They offer a refund so invite you to provide them with your bank details. The flight is not cancelled at all. These evil thieves have caused her distress but her husband checked it out and found it to be a scam.
We must all be aware as we’ll probably be their next targets.
I’m wondering how the scammers knew her flight details. It looks like nothing is sacred anymore.