Until now, Chinese who wanted to find out what was going on in the world used a VPN called Astrill.

However, it seems the Chinese authorities have wised up to an Apple app which connects iPhone users to Astrill.

On Monday, virtual private network (VPN) provider Astrill sent a message to users of its iPhone app, informing them that the Great Firewall was blocking all VPN protocols "using machine learning".

That message notes that Astrill is working on a new app for iOS 9 that should "overcome this blockage." Other VPN services are unaffected, but Astrill users are finding themselves unable to use the service as they normally would.

VPN services have struggled to operate in China for years because of the Great Firewall and they've faced additional struggles as the country has upgraded its censorship system.

One of the reasons that VPNs have existed in China for so long is that corporates use VPNs to access secure email servers among other functions. Messing around with these could mean that the Chinese might end up hurting their own companies or hacking off big foreign investors.

With VPNs being targeted, many companies, especially small-and-medium sized enterprises, may find it impossible to use the internet for simple everyday business tasks.