Reverse engineering is the process of analyzing a product or process in order to duplicate it. It's often claimed, most notably by Bob Lazar, that this is what is going on at Area 51, where the US government and its military are attempting to reverse engineer captured alien spacecraft.
The big weakness in this process is not knowing the manufacturing tolerances required and exact material specifications involved in order to successfully replicate the "original".
 Technology of a lunar civilization, yeah right...
- "The Apollo crews [brought] back to NASA laboratories not just rocks, but actual samples of the ancient technologies they found—for highly classified efforts at 'back engineering.' " --Dark Mission, p.60 2nd edn.
The most important feature of that passage is that it is presented without a scintilla of evidence, either on page 60 or anywhere else in that catastrophically inaccurate work.