Originally Posted by
daniellam
They are only scanning the boarding passes to make sure that they are not fake (eg. an online check-in boarding pass may be edited before printing).
SecureFlight fields are only used BEFORE YOU CHECK-IN for matching your name against the no-fly lists.
It becomes irrelevant after you check-in as you wouldn't have received a boarding pass in the first place had you either not provided the required SecureFlight information, or if your name matches the no-fly list.
Having a bar code on a boarding pass is not a requirement at this time. Boarding passes issued at the counter on legacy stock rarely have bar codes on most airlines.
There is nothing to stop someone from printing their BP at home, changing the content, printing a new copy and just slicing off the bar code.