They use the smuggled radios to access foreign news and cultural programming.
Some voice concerns over the fairness of the exams and potential problems for traveling to exam sites.
A voluminous U.N. inquiry report finds massive rights abuses in North Korea.
The move is part of a relentless crackdown on allies of Jang Song Thaek.
A new system will require households to sell skins from their slaughtered animals to the authorities, sources say.
The changes dampen military exercises and delay cadre replacements in the ruling party.