U.S. security authorities have intercepted computer shipments and hacked Microsoft's error reporting system to infiltrate hard-to-hack targets, according to revelations over the weekend in German magazine Der Spiegel.
The latest leaks lift the lid on the activities of the National Security Agency's (NSA) Tailored Access Operations (TAO) unit, an elite group of specialists working at "getting the ungettable".
Formed in 1997, when not even 2 percent of the world's population had internet access, the TAO unit has contributed "some of the most significant intelligence our country has ever seen," Der Spiegel cited documents as saying. The unit has "access to our very hardest targets", the NSA paper goes on to say.
The TAO arm uses increasingly sophisticated methods of obtaining information and infiltrating the weaknesses of major IT firms such as Cisco and Huawei, the magazine reported. But it is two of the simpler spying methods that have hit the headlines.
(Read more: World of spycraft: NSA infiltrates gamers' data)
Microsoft error message tapped
Der Spiegel reported that hackers exploited the weakness in Microsoft's error reporting message, familiar to many users of the Windows operating system, that pops up when software crashes, in order to obtain information.
The reporting system is used by Micrsoft engineers to fix bugs and improve software, but NSA hackers use it as a way to capture data sent out from the computer.
NSA agents have also made jokes at the expense of the Seattle-based software giant, Der Spiegel reported. In one graphic seen by the German magazine, the spies replaced the original text of Microsoft's error message with one that read: "This information may be intercepted by a foreign sigint (signals intelligence) system to gather detailed information and better exploit your machine."
Microsoft defended its system and said users who report errors send "limited information" that is used to improve customer experiences.
"Microsoft does not provide any Government with direct or unfettered access to our customers' data. We would have significant concerns if the allegations about Government actions are true," the company told CNBC in a statement.
The specialist TAO unit was expected to infiltrate 85,000 computers worldwide, according to details in Washington's current budget plans for US intelligence services.
Intercepting computer shipments
NSA spies have also stuck to traditional spying methods to carry out their tasks. TAO intercept shipping deliveries or computers or related accessories. The shipment is diverted to a secret NSA workshop and software that can allow agents to track users remotely is installed.
The technique known as "interdiction" is the spy agency's "most productive operations", Der Spiegel cites a document as saying.
—By CNBC's Arjun Kharpal: Follow him on Twitter