To catch a mole: Undercover Dateline NBC reporter outed at DefCon

Found at Reddit, this report of an NBC Dateline reporter who tried to pose as a regular attender (i.e. not wearing the PRESS badge), taking pictures and recording people without warning them that in fact she is a reporter and that they may be on the record.

Read more about it here or on the wired blogpost about it.

This is the movie I first found about it, showing how it all came to be: