While the US has been claiming that the Chinese have been covertly implanting interception tools in US servers heading overseas, it seems that the US government has been doing the same thing. Glenn Greenwald, in an extract from his new book about the Snowden affair, No Place to Hide said that for years the US government loudly warned the world that Chinese routers and other internet devices were a "threat" because they are built with backdoor surveillance functionality that gives the Chinese government the ability to spy on anyone using them. 

But while American companies were being warned away from supposedly untrustworthy Chinese routers, foreign organisations would have been well advised to beware of American-made ones. In June 2010 report from the head of the NSA's Access and Target Development department said that it routinely or intercepts routers, servers and other computer network devices being exported from the US before they are delivered to the international customers. It then implants backdoor surveillance tools, repackages the devices with a factory seal and sends them on. The NSA thus gains access to entire networks and all their users. 

The implanted device connects back to the NSA and according to the report after several months, a beacon implanted through supply-chain interdiction will call back to the NSA covert infrastructure. This call back provided us access to further exploit the device and survey the network. Greenwald’s theory is that the US was warning about Chinese hacked servers because it was worried that the cheaper models were replacing the US hacked models.