Skype.com (503,932 censored, 0 allowed) and live.com IM services were blocked with 100% denial rates at all times. During the August 3, 2011 protest events Skype accounted for up to 29.24% of all censored traffic; 9% of Skype requests were software update attempts, which were also denied, confirming content-agnostic domain-level blocking rather than content-selective filtering.

Four circumvention tool names were explicitly blocked as URL substrings with zero allowed requests passing through: hotspotshield (126,127 blocked), ultrareach (50,769), ultrasurf (31,483), and the generic keyword israel (48,119). All matching requests — including update checks and background pings — were denied at 0% pass-through rate.

§5.4, Table 9 detection

Syria's Blue Coat proxies blocked any URL containing the string "proxy," generating 3,954,795 censored requests (53.61% of all policy-censored traffic in Dfull). The collateral damage was severe: Google Toolbar's /tbproxy/af/query API calls and Facebook social plugins (/plugins/like.php at 43.04% and /extern/login_status.php at 38.99% of facebook.com censored traffic) together account for over 80% of censored facebook.com requests, all denied with 0 allowed counterparts.

§5.4, Tables 9 & 14 detection

Syrian censors used a custom Blue Coat URL-category to policy_redirect specific Facebook pages (Syrian.Revolution: 1,461 censored) while allowing 17.70M facebook.com requests overall — only 1.62M (8.4%) were censored. The URL-pattern matching was imprecise: www.facebook.com/Syrian.Revolution?ref=ts was blocked but the identical page with additional AJAX query parameters (__a=11&ajaxpipe=1) was not categorized as 'Blocked Site,' leaving some access through.

§6, Tables 12–13 detection

Port 9001 (Tor) ranked third among all blocked ports in Syria, behind only ports 80 and 443. Proxy SG-48 was responsible for a disproportionate share of Tor censorship — blocking Tor traffic for multiple consecutive days — while other proxies in the same deployment did not, indicating per-proxy policy specialization or traffic steering of suspected circumvention flows to dedicated blocking infrastructure.

§4 (Ports), §5.2 detection

IRBlock discovered that 1.7M of 3.3M blocked apex domains (52%) were attributed to blanket suffix-level blocking rules rather than individual domain listings. Examples include regex patterns targeting all Israeli domains (.il TLD), adult content (.porn), and country-coded suffixes (.com.mx, .my.id). Of 87K Tranco-ranked apex domains analyzed, 37% fell into adult content, with entertainment and gambling following. Approximately 1.27M apex domains were jointly censored by both DNS and HTTP filters, while the two filters maintained operationally independent blocklists for a significant fraction of domains.

2025-tai-irblock §5.3 dns-poisoningip-blockingkeyword-filtering

For Tier 2 apps (IP geo-blocking only), using a VPN with a foreign endpoint was sufficient to restore access. For Tier 1 apps (SIM + IP geo-blocking), the authors confirmed that (1) removing the Indian SIM card and accessing via WiFi, or (2) intercepting HTTP traffic with a MITM proxy to suppress or rewrite the carrier_region=IN parameter, fully bypassed server-side censorship. The authors note that Indian users primarily rely on mobile Internet, making SIM removal impractical as a user-facing solution.

2024-gosain-out §4.3, §5 ip-blockingkeyword-filtering

After India imposed a permanent ban in January 2021, seven of the eight previously SIM-only-blocked apps escalated to dual-factor filtering: they continued extracting carrier_region=IN from the SIM card while simultaneously adding IP geo-blocking. Accessing these apps now requires both a VPN (for source IP masking) and SIM removal or carrier_region parameter suppression; MICO Chat remained the sole app using only SIM-based blocking.

2024-gosain-out §4.3 (Permanent ban subsection), Table 2 ip-blockingkeyword-filtering

Seven of the 220 banned apps (Tier 1, including TikTok, Likee, Kwai, UC Browser, FaceU, Hago, and V-Fly) used the Android TelephonyManager.getSimCountryISO() API to read the primary SIM's country code and embed a carrier_region=IN parameter in HTTP requests, enabling server-side identification and blocking of Indian users regardless of source IP or VPN state. A dual-SIM phone with an Indian SIM in the secondary slot only (primary empty or non-Indian) bypassed the check.

2024-gosain-out §4.3 ip-blockingkeyword-filtering

GFWeb tested 1.02 billion domains against the GFW over 20 months and discovered 943,000 pay-level domains blocked by HTTP filters and 55,000 by HTTPS filters — the largest GFW blocklist dataset ever published. The HTTP-to-HTTPS ratio (17:1) confirms that the GFW's HTTPS keyword-based and SNI-based blocking covers far fewer domains than its HTTP host-header blocking, likely because HTTPS blocks carry higher collateral-damage risk.

2024-hoang-gfweb Abstract, §5.1 dpidns-poisoningip-blockingkeyword-filteringsni-blocking

The largest measurement study of Turkmenistan censorship to date tested 15.5 million domains and found more than 122,000 domains censored using separate blocklists for DNS, HTTP, and HTTPS. Reverse-engineering the blocking rules revealed approximately 6,000 over-blocking rules that cause incidental filtering of more than 5.4 million additional domains — a 44x collateral damage ratio relative to intentionally blocked domains.

2023-nourin-measuring §Results dns-poisoningdpikeyword-filteringip-blocking