Characterizing Web Censorship Worldwide: Another Look at the OpenNet Initiative Data

Residential ISP vantage points detect 36% more blocking than academic networks: of 1,947,691 matched URL tests, 72,454 non-academic tests were classified as blocking versus 52,921 academic tests. Averaged across 10 countries, the Jaccard similarity between blocked-URL sets in academic vs. non-academic networks is 0.59, indicating substantial divergence.

§5.3, Fig. 12 evaluation measurement-platform

Iran's censorship infrastructure shifted from fully decentralized (Jaccard similarity ~0 across ISPs in 2007) to highly centralized by June 2011, when the Jaccard similarity between the national gateway AS 12880 and two other ISPs reached 0.94 and 0.95. Almost all 2011 blocking was accompanied by a blockpage containing an iframe redirecting to internal IP 10.10.34.34, providing direct evidence of a single choke-point filtering infrastructure.

§4.5, Table V detection dpipacket-injection ir

Locally curated URL lists elicit 3–5× higher blocking rates than global lists in high-censorship countries. In China and Yemen, local content was blocked three to five times more than globally sensitive content, attributed to language filtering and active censorship of local political discourse; China's 99% block rate on 'falun' in HTTP path vs. 81% for 'falun' in domain name further illustrates trigger sensitivity.

§5.4, §4.9, Fig. 13 evaluation keyword-filteringdpidns-poisoning cn

Across MENA countries (UAE, Tunisia, Oman, Iran, Qatar, Yemen, Saudi Arabia, Burma), over 80% of blockpage-delivering tests delivered the blockpage without DNS redirection, indicating transparent web proxies performing deep HTTP inspection rather than the cheaper DNS-intercept approach dominant in China. McAfee SmartFilter was identified in Qatar, Saudi Arabia, and UAE; Netsweepr in Qatar, UAE, and Yemen.

§5.1, Table VI evaluation dpipacket-injectiondns-poisoning aeirsacn

Yemen's national ISP (YemenNet) uses explicit blockpages for social and Internet-tools content while applying stealthy techniques — TCP RST injection and unrequited HTTP GETs — specifically for political and conflict content that is constitutionally protected. Censorship also ceases intermittently when the ISP exhausts filtering product licenses.

§4.2, Fig. 6 detection rst-injectionpacket-injectiondpi generic