http://en.wikipedia.org/wiki/ROKS_Cheonan_sinking

http://english.hani.co.kr/arti/english_edition/e_editorial/615515.html

http://www.northkoreatech.org/2011/01/14/south-korea-steps-up-blocking-of-dprk-sites/

http://www.northkoreatech.org/2010/10/21/south-korea-now-blocking-new-kcna-site/

http://www.northkoreatech.org/2010/12/23/south-seeks-block-on-dprk-internet-propaganda/

http://www.northkoreatech.org/2011/09/18/south-koreas-online-blocking-sharply-rose-in-2010/

http://koreajoongangdaily.joins.com/news/article/article.aspx?aid=2943115&cloc=joongangdaily%7Chome%7Cnewslist1

http://koreajoongangdaily.joins.com/news/article/Article.aspx?aid=2943052

http://english.yonhapnews.co.kr/national/2011/10/19/54/0302000000AEN20111019005800315F.HTML

http://atimes.com/atimes/Korea/MJ26Dg01.html