2020-raman-censored
findings extracted from this paper
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Censored Planet collected 21.8 billion measurements over 20 months from more than 95,000 vantage points in 221 countries, covering 66–173 more countries than OONI and ICLab, with a median of 8 ASes per country versus OONI's 4 and ICLab's 1. In March 2020, it achieved coverage of 9,014 ASes compared to OONI's 1,915. Censored Planet and OONI together covered all 21 countries rated 'Not Free' by Freedom House, while ICLab reached only 4.
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Of 21.8 billion raw measurements, approximately 7% (1.5 billion) were initially flagged as blocked; iterative HTML clustering and DBSCAN image clustering then removed ~500 million false positives, leaving ~1 billion confirmed blocked measurements. The clustering process formed 457 new response clusters, of which 308 were confirmed blockpages and 149 were false positives, with Cloudflare bot-checks being a notable source of false positives in HTTPS measurements.
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Mann-Kendall trend analysis at 99% significance on 20 months of data found increasing censorship activity in more than 100 countries, driven primarily by DNS and HTTPS blocking methods, and identified 11 website categories facing rising censorship including human rights content, news media, and provocative attire. Countries such as Norway (ranked #1 in press freedom) showed aggressive DNS blocking across 25 ASes targeting more than 50 domains in at least 6 categories including hrw.org.
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Censored Planet achieves 93% /24 vantage-point continuity and 99.01% AS continuity between weekly scans, versus ICLab's 64% and OONI's 36% AS continuity. Applying bitmap-based anomaly detection on the resulting longitudinal time series detected 15 prominent censorship events over 20 months, two-thirds of which had not been previously reported, while OONI data showed no corresponding increase for most newly discovered events due to sparse volunteer measurements.
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During the Sri Lanka social-media block following the April 21, 2019 bombings, Censored Planet measured HTTP(S) censorship jumping from 0.1% to 2% in one week and discovered 22 blocked domains versus the 7 reported by NetBlocks and AccessNow; 5 of those extra domains were only present in the Alexa top-sites list, not the Citizen Lab Global Test List. Blocking remained elevated through May 12, 2019, contradicting public reports that the ban was lifted by May 1st.