There's plenty we already know about student debt: We all tend to have a lot of it (trillions of dollars are owed in the U.S. alone), it's tough to pay back (especially when you don't owe a lot) and it obviously makes us all cry a lot.

The findings from University of Michigan Economics Professor Susan Dynarski add another layer to this cake of financial shame: Most of the debt from recent years is not from the folks heading out to expensive four-year schools, but from the slightly less-expensive for-profit college industry.

What's so bad about for-profit schools?

Studies show that students with less debt are more likely to have problems paying that debt back because their degrees (or lack-thereof if they dropped out) are earning them less money once they hit the working world.

For-profit schools, with their dicy history (even lambasted by John Oliver earlier this year), are notorious for saddling students with more debt than a four-year state school without any of the guaranteed post-grad salary benefits.

The National Association for College Admission Counseling describes the for-profit college model as colleges "run by companies that operate under the demands of investors and stockholders. These institutions are privately run and exist, at least in part, to earn money for their owners. Nevertheless, for-profit colleges can receive up to 90 percent of their revenue from federal student aid."

The U.S. Government Accountability Office sent undercover applicants to investigate 15 for-profit colleges and found that all 15 used some dubious tactics to get students (mostly from low-income backgrounds) to register for classes. Four schools reportedly asked the students to lie on their financial aid forms to get more federal aid and all of the schools had "questionable" strategies for recruiting students.

Recruiters routinely ~decorated the truth~ about the kinds of salaries students would see post-grad, refused to give straight answers about how long the programs would last, how much they'd cost to complete and how likely they were to graduate -- even though there are federal regulations that require them to provide that kind of information.

There have also been several cases of these schools (mostly national chains) closing down their campuses when things start to go south, leaving students with all the debt and none of the job prospects.