One is proper lying, and the other is lying by omission.

What do you mean by "difference" between them? Morally? I suppose lying straight up is more likely to be morally dubious, whereas one might argue that lying by omission is more acceptable, depending on the circumstances. With the former, you're knowingly committing an act of deception, whereas with the latter, you're merely failing to act where you probably ought to.

Or do you mean difference in technique? The former is harder.

Why do you want to know these things?