An excerpt of investigative reporter Glenn Greenwald's new book No Place to Hide published today in The Guardian asserts that the National Security Agency "routinely" bugs computer network equipment made in the United States and sent to customers abroad:
A June 2010 report from the head of the NSA's Access and Target Development department is shockingly explicit. The NSA routinely receives – or intercepts – routers, servers, and other computer network devices being exported from the US before they are delivered to the international customers.
The agency 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 document gleefully observes that some "SIGINT tradecraft … is very hands-on (literally!)".
The excerpt doesn't say whether the bugging was done to entire shipments of equipment (as opposed to individual items ordered by specific surveillance targets).