The Great Firewall of China has recently been upgraded to combat the use of VPNs to circumnavigate the blocks it puts in place.
[quote=Astrill]Astrill blamed a technology update to the Great Firewall (GFW), saying the system now has the “ability to learn, discover and block VPN protocols automatically”[/quote]
For example, if a lot of encrypted traffic passes through the GFW to a certain server outside China, the GFW can notify staff to manually review it and block the server based on its IP address if they so choose. It can also be automatically blocked.
Read more: http://www.securityweek.com/great-firewall-upgrade-troubles-vpn-users-china