Overuse brings problems for young adults and teenagers, Yang Yang reports.

After yet another late night spent browsing the Internet, Tracy Zheng, a 30-year-old PhD student at Nanjing University, swore to stop wasting time she could hardly spare.

"I had a lot of books and papers to read, but instead I wasted my time online." She said she spends about five hours a day reading micro blogs, Lily BBS - a site for students at her university - and other sites.