High Yield Investments

Is HYIP (HIGH YIELD INVESTMENT PROGRAM) legal in the united states?
My impression is that they are all scams. It is just not possible to offer interest rates like that. I certainly wouldn’t invest in one outside the U.S., because it would be hard to get your money back when they steal it. But I wouldn’t invest in one inside the U.S. either. Here is a government website about these scams:
Chinese High Yield Nuclear Test