In a Fox news article entitled "German magazine claims NSA hacking unit uses powerful methods to obtain data", a magazine article in Der Spiegel is cited as claiming, among other things:
...if the NSA tracked a target ordering a new computer or other electronic accessories, TAO could tap its allies in the FBI and the CIA, intercept the hardware in transit, and take it to a secret workshop where it could be discretely fitted with espionage software before being sent on its way.
Intercepting computer equipment in such a way is among the NSA's "most productive operations," and has helped harvest intelligence from around the world, one document cited by Der Spiegel stated.
The first paragraph contains the weasel word "could". Of course they could. In a way it would not be terribly surprising, one might expect such an opportunity to be seized when monitoring serious criminal or terrorist activity if due process permits.
The second paragraph says that this is "among the NSA's most productive operations". To me, that implies that they do this a lot, and/or that it has obtained notable results.
However, from Fox this is now 3rd hand information (Document --> Der Spiegel --> Fox) and I wondered about credibility of such a document that the news article itself does not identify.
Also, another portion of the article claims that US products contain known exploits that secret agencies are well aware of -- indicating to me that physically intercepting a new computer order would perhaps be unnecessary.
Can a hidden source reasonably support a claim of hardware interception?
Are there any other credible reports that support this claim?