Twitter's country-withheld content mechanism relies on a browser-set location cookie, not IP geolocation; the authors confirmed that viewing a known-withheld Turkish tweet via a Turkish proxy server did not trigger the withholding display, but manually changing the Twitter app's location setting to 'Turkey' did — meaning any Turkish user who sets their location to a different country can bypass the entire withholding mechanism without Tor or a VPN.

Among withheld retweets in the Turkish dataset, 92% of the corresponding original tweets were also withheld, while 4% survived uncensored and 4% belonged to fully-withheld accounts; this asymmetry suggests the Turkish government's censorship targeting mechanism operates with some degree of systematic (possibly hashtag- or keyword-based) sweep rather than purely manual per-tweet review.

§5.2 (Phase III) detection

Manual review of 46 fully-withheld Turkish accounts found that 36 (78%) were classified as posting anti-government political content critical of President Erdoğan, 2 as pornography, 1 as advertising bots, 3 as unidentified, and 4 as no-longer-findable; NMF/tf-idf topic modeling of withheld individual tweets confirmed that the dominant censored themes were criticism of government-aligned media and ruling-party politicians.

§6.1, §6.2 evaluation

The Chilling Effects database contained only 33 notices from Twitter across all countries, far fewer than the 108 account-withholding requests disclosed in Twitter's own transparency reports for the same period; Twitter itself acknowledges its transparency reporting is neither 100% comprehensive nor complete, and the authors confirmed that at least 86% of Turkish government withholding requests for non-protected tweets were approved by Twitter.

§3.1, §4.2 policy

Twitter's official transparency reports for Turkey recorded 183 withheld tweets (Jan–Jun 2014) and 1,820 withheld tweets (Jul–Dec 2014), but the authors' collection of 17 million geo-bounded Turkish tweets yielded 3,258 withheld tweets from the streaming phase alone, and expanding to followers of censored accounts produced 171,652 withheld tweets—roughly two orders of magnitude more than Twitter's own disclosures.

§4.1, §5.2 evaluation

The June 2025 Iran shutdown—carried out during the Iran-Israel war beginning ~June 19—did not use BGP route withdrawals as in 2019. Instead, authorities applied service-level restrictions at the national border: DNS poisoning of foreign destinations, protocol whitelisting permitting only pre-approved domestic services, and DPI to block circumvention-tool traffic. Iran's international traffic fell roughly 90% while the country's BGP routes remained advertised, making the shutdown invisible to BGP-based monitoring systems. OONI measurement volume, which totalled 121,333 in June 2025, collapsed to under 200 submissions on June 19-20.

2025-iran-shutdown-measurement Executive Summary / §2 dpidns-poisoningport-blockingip-blocking

Article 19 documents that Iran's National Information Network (NIN / SHOMA) was designed with explicit reference to China's Great Firewall as a model, with institutional mirroring: Iran's Supreme Council of Cyberspace parallels China's Cyberspace Administration of China, and both governments share a "cyber sovereignty" doctrine used to justify domestic content controls and cross-border technology transfer. The report frames Iran's filtering infrastructure as deliberately architected to replicate GFW capabilities, not as an independently developed system.

2026-article19-tightening-the-net §2, §3 dpisni-blockingdns-poisoningip-blockingbgp-hijackthrottling

Article 19 documents that Iran combines technical filtering with formal coercion of major foreign platforms (including Telegram, Instagram, and WhatsApp) to comply with content removal orders under threat of full blocking. The report notes that Iran's 2022 Women Life Freedom protests accelerated platform blocking when foreign operators refused compliance, demonstrating that the censorship system operates in two modes: coerce-and-allow for compliant platforms, block for non-compliant ones. Domain fronting via these platforms is therefore subject to sudden revocation if political conditions change.

2026-article19-tightening-the-net §6 ip-blockingdns-poisoningthrottling

Brussee measures a systematic pattern of Chinese government websites actively blocking access from outside China (the "reverse Great Firewall"), publishing a CSV dataset of affected domains (available at zenodo.org/records/18172145). The paper frames this outbound geo-blocking as a cybersecurity-motivated practice — Chinese authorities classify foreign access to domestic government infrastructure as an attack surface — distinct from the inbound information control goal of the GFW.

2026-brussee-reverse-great-firewall §3, §5 ip-blockingasn-blackholing

Brussee develops a conceptual framework distinguishing two logics of government geo-blocking: (1) information control (blocking inbound foreign content from domestic users) and (2) data sovereignty / attack-surface reduction (blocking outbound access by foreign actors to domestic systems). Chinese government site blocking of external IPs is motivated primarily by the second logic, creating an asymmetric internet topology where CN citizens cannot reach the outside world, and outside actors cannot probe CN government infrastructure.

2026-brussee-reverse-great-firewall §2, §4 ip-blockingasn-blackholing

ShieldShare demonstrates that an Android application can route all hotspot-client traffic through a VPN tunnel without root access by using a SOCKS5/HTTP/HTTPS proxy layer between the hotspot and the VPN, with per-client traffic accounting and quota management. The system works because Android's native hotspot does not forward VPN routing tables to connected clients; ShieldShare interposes a proxy that handles this. Released as open-source.

2026-edorh-shieldshare §Abstract ip-blocking