sentences:  On 26 July 2011, a hacking incident of SK Communications (owner of NateOn, South Korea's most popular messenger) took place, during which about 70% of all Korean citizens' numbers were hacked.As a result, all South Korean websites were obliged to delete and are no longer allowed to use the number except for payments.The RRN has since replaced the number with identification SMS (via phone owners' information), public key certificate (requiring a visit to a bank, since PKC is stored in user's PC or personal device unlike other countries), and i-PIN, Internet Personal Identification Number, which may be obtained via registration of RRN with a governmental site.