Are all of the K-girls here on fraudulent student visas?

It's been in the news last year that there were a few 'schools' in K-town that were just fronts to get people student visas who never attended school. Many of the Korean providers have entered the country on these fraudulent student visas and are now working in AMPs all across the country.

I was wondering if all of them are on these kinds of visas? If the loopholes for this kind of illegal immigration are ever closed will the supply dry up? There must be 10's of thousands of Korean girls living and working in AMPs with visas like that.