This article illustrates how difficult it can be for someone other than the original component manufacturer to authenticate parts. …
Reverse engineering a counterfeit 7805 voltage regulator
The author explains how a specific microcircuit chip works, including a description of the operation of transistors contained in the chip. As the author explored the chip design, he found reasons to suspect the chip was counterfeit and produced by someone other than the OCM indicated by the marking on the device. Later, however, the author learned that his conclusion was likely incorrect.
Lesson: In the absence of authentication support from the OCM, expertise in electronic part forensics and research is necessary to determine counterfeits from authentic electronic parts.