Iran blocked Tor handshakes using Deep Packet Inspection (DPI) in January 2011 and September 2011. Bluecoat tested out a Tor handshake filter in Syria in June 2011. China has been harvesting and blocking IP addresses for both public Tor relays and private Tor bridges for years.
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Jacob Appelbaum, Roger Dingledine: How governments have tried to block Tor
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