Since the 1870s, journalists have been posing as patients or attendants to expose horrid conditions and treatment inside mental hospitals. Nellie Bly, incidentally, was not the first. 

These are examples of undercover reportage that were considered to have crossed ethical lines or that caused major legal wrangles.

Medicare and Medicaid fraud have been perennial reporting topics since the 1960s, often requiring undercover techniques to amass specific details.

Reporters have worked as guards or gotten themselves arrested -- sometimes with the aid of authorities and sometimes without -- to investigate conditions inside prisons and jails.