The Tailored Access Operations cyberwarfare intelligence-gathering unit, which is supposed to gather information on computer systems used by non-U.S. entities, has attacked the firmware in hard drives made by Western Digital Corp., Seagate Technology PLC, Maxtor Corp. and Samsung Electronics Co., all of which except for Samsung are U.S. companies, the magazine said.
Operating at a former Sony Corp. computer chip factory in San Antonio, TAO describes itself as "getting the ungettable," Der Spiegel said, citing leaked documents that say the unit -- one of the most secretive branches in a secretive agency -- also exploits technical weaknesses to hack into systems of information technology giants, including Microsoft Corp., Cisco Systems Inc. and China's Huawei Technologies Co., the world's largest telecommunications equipment maker.
"It is not about the quantity produced but the quality of intelligence that is important," a former TAO chief wrote, describing her work in a document Der Spiegel cited.
The document quotes a former unit head as saying TAO has contributed "some of the most significant intelligence our country has ever seen."
Spyware TAO sometimes plants on intercepted equipment deliveries, which lets it gain remote access to the computer systems once they are delivered and installed, the magazine said.
The remote access happens through so-called backdoor malware programs, which bypass normal authentication and secure illegal remote access to computers, hard drives, routers and other devices, the magazine said.
In these and other ways, "it appears the U.S. intelligence agency is compromising the technology and products of American companies," Der Spiegel said.
The magazine described a 50-page product catalog of tools and techniques an NSA division called ANT, which stands for Advanced or Access Network Technology, uses to gain access to devices.
The ANT division plants malicious code in so-called BIOS, or the Basic Input/Output System, of software located on a computer's motherboard that is the first thing to load when a computer is turned on, said the magazine, which previously reported on documents leaked by former NSA contractor Edward Snowden.
Sunday's report did not cite Snowden but said it was partly compiled by Laura Poitras, who collaborated with Snowden on the disclosure of the NSA's collection of phone data of thousands of Americans and overseas intelligence targets.
The NSA's phone data-collection program was ruled legal by a federal judge in New York Friday, days after a federal judge in Washington declared it unconstitutional and "almost Orwellian."
The NSA declined to comment on Sunday's magazine report, but said the TAO unit was key to national defense.
"Tailored Access Operations is a unique national asset that is on the front lines of enabling NSA to defend the nation and its allies," the NSA said in a statement.
"We won't discuss specific allegations regarding TAO's mission, but its work is centered on computer network exploitation in support of foreign intelligence collection," the statement said.
Microsoft said it "does not provide any government with direct or unfettered access to our customer's data," adding, "We would have significant concerns if the allegations about government actions are true."
Cisco said in a blog post Sunday: "At this time, we do not know of any new product vulnerabilities, and will continue to pursue all avenues to determine if we need to address any new issues. If we learn of a security weakness in any of our products, we will immediately address it. As we have stated prior, and communicated to Der Spiegel, we do not work with any government to weaken our products for exploitation, nor to implement any so-called security 'back doors' in our products."
None of the other cited tech companies had immediate comment on the report.