Heo Hyun-hye, a 31-year-old office worker in Seoul, was dumbfounded when her smartphone’s messaging application Kakao Talk automatically added the phone number of a guy she once had contacted for a blind date. She didn’t know about it until the guy actually said hello to her through the messenger app.

“You don’t feel very comfortable if a guy you want to forget says hello to you,” Heo told The Korea Herald. Because she had deleted the guy’s number, she never expected to see him on the mobile messenger.

“What’s sillier is that the guy had thought like me, too. The guy told me that he deleted my number from his phone but I was on his messenger list. That’s why he said hello to me to ask if I hadn’t delete his number,” she said.

Feeling uncomfortable, Heo said she would delete her Kakao Talk account and wipe out the application for good, although many of the other 2 million Korean smartphone owners are using the app.

Heo’s case is just one of the many privacy loopholes in social networking services that can be personally intimidating or exploited commercially...