Counterfeit materials are the most frequently encountered danger to the supply chain that delivers U.S. military systems.

Because technology often touches many hands in many foreign countries before reaching a contractor, malicious actors or scammers have multiple opportunities to taint materials, says a GAO report.

The GAO reported that vendors in China are marketing to the Pentagon suspected counterfeit electronic components. After ordering military-grade parts from online portals, government investigators masquerading behind a fictitious company received 40 price quotes for bogus part numbers -- all from vendors located in China.

To guard against compromised technology, which potentially could fail or harbor malware, acquisition specialists are forging new relationships with the intelligence community, said a Pentagon official. The Defense Intelligence Agency has conducted about 500 analyses for military purchasing programs, he said during a House Energy and Commerce Subcommittee on Oversight and Investigations hearing. A robust trusted systems and networks strategy for limiting supply risks is expected to be operational by fiscal 2016, the official added.

GAO's online shopping experiment focused on defense components that are hard to find, including those used in weapons systems. When the auditors asked vendors for invalid part numbers that GAO had concocted, the firms sent the auditors bogus parts labeled with the invalid numbers. In other words, the Chinese suppliers -- six of them -- offered to sell parts that do not technically exist. The trial ran from August through February.