SEOUL, South Korea — K-pop. Cheating on exams. Even pornography.

North Korea on Tuesday warned against the disruptive influence it said smartphones could have on its isolated population, as the devices have begun to expose young people in particular to information and trends from the outside world.

In the hermetically sealed North, South Korean officials estimate that the number of mobile phones has risen to six million since 2008, when cellular phone service began as a joint venture between the Egyptian telecommunications firm Orascom and the North’s communication ministry. The country has a population of 25 million.

On Tuesday, the North’s main state-run newspaper, Rodong Sinmun, published an article listing what it called “negative repercussions” from the introduction of smartphones in schools around the world, including the use of phones during classes, cheating during exams and the circulation of pornographic material.

“This proves that mobile phones have become an avenue to instill students with unhealthy ideology,” it said. “Most educators and parents around the world believe that various corrupt and reactionary cultures spreading through mobile phones are confusing students as they shape their lives’ values.”