It's a connected world, so online activities are probably pretty grey-areas. If you defraud someone (for example) but they're in another country, where did the crime happen?
The US-USA extradition treaties have always been one way.
I thought extradition laws usually had some kind of clause like "only applies if it'd be a crime in both jurisdictions", but now I think about that I can't remember where I heard that or why I think it so I will admit complete ignorance.