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.