Checkpoints and Borders Policy Debate - Unauthorized boarding/security breach at SFO?

A friend flew SFO-EWR tonight (Sat July 14), and tells me that they were three hours late because of a security breach: apparently someone walked past gate agents and boarded the plane with a boarding pass for another flight. She said they sat at the gate for two hours and were then made to disembark and reboard.

Anyone hear about this? A cursory search hasn't turned up any news coverage, and I'd love to hear the details...UAL was keeping pax in the dark.

I believe the flight was UAL516, but am not sure. (My friend missed her flight to GVA and was given a boarding pass for UAL956 with a boarding time 10 hours before departure, but that's neither here nor there.)

Since when does this constitute a security breach? Last month, I was sitting in seat 1A and watched over a dozen folks walk onto the wrong flight (dual gate at DFW) - one was even sitting in a seat when the actual flight's passenger walked on and wondered why there was already someone there.

We weren't all kicked off the airplane and made to reboard - they simply amped up the destination announcements.