Topics of Controversy: an Empirical Analysis of Web Censorship Lists
Proceedings on Privacy Enhancing Technologies ; 2017 (1):42–61 Zachary Weinberg*, Mahmood Sharif, Janos Szurdi, and Nicolas Christin Topics of Controversy: An Empirical Analysis of Web Censorship Lists Abstract: Studies of Internet censorship rely on an exper- Internet was evolving into a widely-available medium imental technique called probing. From a client within of mass communication [55]. Despite concerted efforts each country under investigation, the experimenter at- to defend free expression, online censorship has be- tempts to access network resources that are suspected come more and more common. Nowadays, firewalls and to be censored, and records what happens. The set of routers with “filtering” features are commonplace [27], resources to be probed is a crucial, but often neglected, and these are applied by governments worldwide to pre- element of the experimental design. vent access to material they find objectionable [1, 21]. We analyze the content and longevity of 758,191 web- Without access to inside information, determining pages drawn from 22 different probe lists, of which 15 what is censored is a research question in itself, as well are alleged to be actual blacklists of censored webpages as a prerequisite for other investigations. Official pol- in particular countries, three were compiled using a pri- icy statements reveal only broad categories of objection- ori criteria for selecting pages with an elevated chance able material: “blasphemy,” “obscenity,” “lèse-majesté,” of being censored, and four are controls. We find that “sedition,” etc. [21, 59]. The exact list of blocked sites, the lists have very little overlap in terms of specific keywords, etc. is kept secret, can be changed without pages.
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