Well... I never heard of such a thing. So I googled. An Enginerering Sample is exactly that: a beta chip, not officially released. It can have various defects, such as being unable to change the multiplier, instability, errors, overheating.. who knows what yours might do. It also seems that some Engineering Samples were unlocked chips, and thus could be overclocked till they blew. Since it's not an official release, the chips were probably stolen from the factory and sold on ebay.