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The men died of malnutrition in 2003 or 2004, he said.

Although information gathered by groups such as ORNK, Daily NK and Good Friends from North Korean sources are widely quoted in South Korean media, questions about the credibility of their informant networks persist.

“It is a mixed picture, because it is essentially a question of how credible marketplace rumors are in any society,” said Andrei Lankov, an analyst on North Korea at Seoul’s Kookmin University. “These informants essentially tell you what the average North Korean in a border area, possibly a minor official, is hearing. In some places, it might be wrong; in other places, they have been proven very correct.”

Mr. Lankov noted that a reporter relying on sources inside the North was the first to break the news of Pyongyang’s flawed currency valuation in 2009.

“I don’t think they fabricate, though their correspondents are not professional,” said Choi Jin-wook of Seoul’s Korea Institute of National Unification. “There are now 20,000 defectors in the South, and they have family, friends and relatives, and they send money and correspond and communicate, so [they] are a major source of information.”

Mr. Choi said relatives of defectors were imprisoned in the past, but corruption now is so rife that North Korean police are bribed to look the other way when money begins to arrive for a family after one of its members defects.

Mr. Ha said he always checks with at least two sources from different geographical parts of his network before publishing anything. In the six years that he has run ORNK, he has dropped 10 percent of his informants after their information proved unreliable, he said.

Meanwhile, a North Korean walked across the heavily mined border into South Korea, Reuters reported Wednesday.

Military and spy agency officials could not explain how the man managed to walk across the 2.5-mile-wide minefield and past North Korean guards. Authorities were interrogating him after South Korean guards picked him up late Tuesday.

Hundreds of North Koreans flee the impoverished country each year across its northern border with China, and most make their way to the South. More than 20,000 have found refuge in the wealthy capitalist neighbor, Reuters reported.