Encrypted Virtual Private Network (VPN) systems have long been the surefire way to get around China's Great Firewall, but that may be changing. The Guardian reports that several VPN providers are saying a new government tool can "learn, discover and block" traffic going through VPNs, and that major ISP China Unicom is automatically terminating connections that are using one. Astrill, one VPN provider, has apparently sent an email warning its customers that common protocols are being blocked, though it says it believes that "this blockage will be removed and things will go back to normal."

This isn't the first time people have reported VPN blocking. Over the past few years, government efforts to police the internet have systematically targeted loopholes in the system, and The Guardian and others reported major crackdowns on VPN use in May of 2011. In many cases, companies simply find new tricks to get around the Great Firewall. But blocking VPNs does more than lock down access to sites like Facebook and YouTube: it also cuts off businesses who use VPNs for secure communication.

One executive complained to Global Times that "you can't block all VPNs without blocking businesses, including Chinese businesses," and that China's commerce-friendly environment was dependent on "modern business infrastructure" like the VPN. That doesn't necessarily mean those businesses will have enough clout to get access restored, but it does seem a particularly bitter pill for them and citizens alike.