Not an urban legend, it's been well publicized, here's a whole congressional hearing on it (warning, it's long): https://www.gpo.gov/fdsys/pkg/CHRG-112shrg72702/pdf/CHRG-112...

Not good enough, here's a few more, but there is plenty else out there: http://www.ibtimes.com/why-pentagon-finding-counterfeit-chin...

http://www.combatcounterfeits.com/gallery.htm

Personal experience having purchased random TO-3 packaged transistors from ebay labeled as LM323K voltage regulators to repair old hardware. Its "well known" in the retrocomputing hobby.

Ironically SOME sellers on ebay are legit, and some sellers are legit sometimes, so if you play a statistical game buying from ten sellers at a 50th the price of legit on-shore sellers, you still save money. Obviously its a lot simpler to build a temporary test fixture for a 70s linear voltage regulator than a memory chip or obscure CPU support chip, LOL.

Idea, adding sub-circuity to a design to detect for bad parts or test for a good part. Would only work for high end designs.