Twitter has issued a message to reassure its users after the social networking site detected "unusual access patterns" that led to "unauthorized access attempts to Twitter user data".
In a statement on Twitter's blog it said that its investigation had detected that attackers may have had access to usernames, email addresses and passwords for around 250,000 users.
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Mr Kim has made two recent visits to China.
The study looked at the development of 422 children over the course of eight years.
The president said they will come into force if China refuses to change its practices.