That's just what I've heard. A few people mentioned it as a theory, and as far as I know the people at Stark's labs are looking into it.

[He's trying to downplay it, but the expression on his face is vaguely nauseous. That's probably telling.]

It wouldn't be impossible if they were advanced enough. Nothing I've seen yet indicates that level of technology, but if they're using magic to conceal it we wouldn't know. What about our memories? It's different in my case, but if they did make us, then how would they manage to transfer thoughts?