9158 version 6.9, in addition to its explicit keyword filter, asterisks out all English alphabet letters in any chat message containing six or more consecutive English letters. Combined with explicit keywords for 'http', 'www', and 'com' on its filter list, this constitutes a blanket URL-suppression mechanism that also incidentally blocks arbitrary English-language communication.

Reverse engineering of four Chinese social video platforms (YY, 9158, Sina Show, GuaGua) yielded 42 keyword lists totaling 17,547 unique keywords. Jaccard similarity clustering shows very little overlap between lists from different companies, consistent with prior work that found only 3% overlap in unique keywords across TOM-Skype and Sina UC (4,256-keyword dataset). This provides the largest unbiased cross-platform evidence that Chinese platform censorship is decentralized rather than governed by a monolithic ruleset.

§5.1 evaluation

Between February and May 2015, YY High received 21 updates and 9158 Chat received 8 updates. Updates correlated directly with current events within days: Zhou Yongkang's name was added to 9158 Chat on May 6, days after his April 3 corruption indictment; YY Normal added and then removed Chinese Christian song titles between April 23 and April 30 during a church demolition controversy. GuaGua does not download keyword updates at all.

§5.3 detection

SVP keyword lists from all four platforms explicitly target both government criticism and collective action, contradicting King et al.'s claim that criticism is tolerated while collective action is suppressed. All four platforms censor Falun Gong and current CPC leaders (including phonetic homonyms like '习尽平'); over 90% of YY's event-related keywords (2,535 total) reference the June 4 1989 Tiananmen Square Massacre, and derogatory phrases such as '共匪' (Communist gangsters) appear alongside collective action event keywords.

§5.2 evaluation

YY version 7.1 silently exfiltrates the full text of any triggering message via HTTP GET to sere.hiido.com, including sending user ID, receiving user ID, and the triggering keyword. The surveillance endpoint authenticates using md5(⌊unix_epoch/1000⌋ + ";username=report;password=pswd@1234") with hardcoded credentials, making the surveillance traffic structurally distinguishable from normal YY traffic.

§4.1.1 detection

During the June 2025 shutdown, Iranian authorities blocked international One-Time Password (OTP) SMS delivery, preventing new sign-ins to foreign secure-messaging platforms and VPN services. This forced users toward government-approved domestic platforms that lack security and privacy protections. The blockade of OTPs effectively weaponized account-recovery flows as a secondary shutdown layer, disproportionately affecting users who needed to activate new circumvention tools during the crisis.

2025-iran-shutdown-measurement §Human Rights Implications port-blockingdpikeyword-filtering

Simple character-level perturbations (English) and homophone substitutions (Chinese), combined with LLM instruction-following prompts directing the model to use word substitutions in its output, successfully bypassed all input and output filters for all 41 input-blocked and 197 output-blocked queries across five major Chinese LLM services (Baidu-Chat, DeepSeek, Doubao, Kimi, Qwen). Every input-blocked query contained at least one keyword combination that alone triggered the filter, confirming keyword-matching rather than semantic classification.

2026-ablove-characterizing §VII-D keyword-filtering

Cross-national experiments conducted from Singapore, South Korea, and Taiwan during February 19–24, 2025 found no variance in blocking implementations, event syntax, or server infrastructure across all five Chinese LLM services. Input blocking was enacted identically in all three international locations, and services connected to the exact same server IP addresses globally — Kimi and Baidu-Chat connected to identical IPs and DeepSeek to the same two addresses across all tested locations.

2026-ablove-characterizing §VIII-A keyword-filtering

Input blocking in Chinese LLM services (DeepSeek, Qwen, Kimi, Doubao) is overwhelmingly consistent: all four services persistently block the exact same queries across all 5 measurement samples in both Simplified and Traditional Chinese. Output blocking is far less consistent, with only 29 out of 349 output-blocked queries blocked across all 5 samples. Baidu-Chat is exceptional: it performs almost no input blocking but instead relies heavily on post-search and output blocking (78.6% of blocks are output-phase).

2026-ablove-characterizing §VI-B keyword-filteringdpi

DeepSeek, Kimi, and Doubao all transmit analytics logs to the same Autonomous System (AS24429, Zhejiang Taobao Network Co., Ltd., a ByteDance/Volcengine subsidiary), with one monitoring endpoint IP directly overlapping between DeepSeek and Doubao. Additionally, all four non-Qwen services maintain connections with servers physically located in China throughout the chat session, transmitting user IDs, session IDs, viewport data, language preferences, and in Baidu-Chat's case, the full query text via URL-encoded CAPTCHA requests.

2026-ablove-characterizing §VI-D keyword-filtering

All five Chinese LLM services transmit partial or complete responses to the client machine even when output blocking is triggered, representing a major information leak. For DeepSeek and Qwen, truncated blocked responses are on average close in token length to full successful responses. For Baidu-Chat, the complete response is transmitted to the client but only partially rendered in the browser UI, with only a word or two visible on screen.

2026-ablove-characterizing §VI-C keyword-filtering