By Holly Yan, CNN/StyleMagazine.com Newswire

The massive college admissions scam, thought to be the biggest ever prosecuted in the United States, is a harsh reminder that wealthy families can cheat their way to even greater privilege. And some say this scandal is just the tip of the iceberg.

Here's what we know so far in this developing case:

Who's involved?

Federal prosecutors say 50 people took part in a scheme that involved either cheating on standardized tests or bribing college coaches and school officials to accept students as college athletes -- even if the student had never played that sport.

Actresses Lori Loughlin and Felicity Huffman are among the dozens of parents facing federal charges. Others charged include nine coaches at elite schools; two SAT/ACT administrators; an exam proctor; a college administrator; and a CEO who admitted he wanted to help the wealthiest families get their kids into elite colleges.

How did this scheme work?

It was all orchestrated by William Rick Singer, CEO of a college admissions prep company called The Key. Singer pleaded guilty to four charges Tuesday and admitted that everything a prosecutor accused him of "is true."

"There were essentially two kinds of fraud that Singer was selling," US Attorney Andrew Lelling said.

"One was to cheat on the SAT or ACT, and the other was to use his connections with Division I coaches and use bribes to get these parents' kids into school with fake athletic credentials."

Here's how the standardized test cheating worked:

Some parents paid between $15,000 and $75,000 per test to help their children get a better score, prosecutors said.

Singer arranged for a third-party -- usually Mark Riddell -- to take the test secretly in the students' place or replace their responses with his own.

How did Riddell allegedly take the tests without being noticed by the test administrators? Singer bribed those test administrators, prosecutors said.

Igor Dvorskiy, who administered SAT and ACT tests in Los Angeles, and Lisa "Niki" Williams, who administered the tests at a public high school in Houston, are both accused of accepting bribes to allow Riddell to take the tests. Both are charged with conspiracy to commit racketeering.

"I want to communicate to everyone that I am profoundly sorry for the damage I have done and grief I have caused those as a result of my needless actions," Riddell said in a statement provided by his attorney. "I understand how my actions contributed to a loss of trust in the college admissions process. I assume full responsibility for what I have done."

Here's how the fake athletic credentials worked:

In some cases, parents allegedly took part in Singer's scheme to bribe college coaches and athletic officials.

While college coaches don't explicitly decide who gets accepted into their universities, they do make recommendations on which recruited athletes should be accepted.

Loughlin, who played Aunt Becky on "Full House," and her fashion designer husband, Mossimo Giannulli, allegedly agreed to pay bribes totaling $500,000 to have their two daughters designated as recruits to the University of Southern California crew team.

But neither of Loughlin's daughters ever competed in crew, a complaint states. Instead, the parents sent photos of each of their daughters on a rowing machine.

How did Singer conceal these massive payments?

Singer disguised bribe payments as charitable contributions to the Key Worldwide Foundation -- a purported non-profit that was actually "a front Singer used to launder the money that parents paid him," Lelling said.

Ironically, Singer -- who allegedly said his goal was to "help the wealthiest families in the US get their kids into school" -- claimed the KWF non-profit was aimed at helping poorer students.

In a 2018, Singer called Loughlin's husband, Giannulli, to clarify the cover story on the family's massive payment.

"So I just want to make sure our stories are the same ... and that your $400K was paid to our foundation to help underserved kids," Singer said.

"Uh, perfect," Giannulli allegedly responded.

What's the reaction been?

Across the country, parents are outraged that wealthy families cheated their way to elite universities -- thereby denying spots for less privileged, harder working kids.

"For every student admitted through fraud, an honest, genuinely talented student was rejected," Lelling said.

The University of Southern California said it has fired senior athletic director Donna Heinel and water polo coach Jovan Vavic, who are both charged in the scheme.

While the university is not directly accused of wrongdoing, "USC is in the process of identifying any funds received by the university in connection with this alleged scheme," it said in a statement. "Additionally, the university is reviewing its admissions processes broadly to ensure that such actions do not occur going forward."

All USC applicants who are connected to the alleged admissions cheating scheme will be denied admission, spokesman Gary Polakovic said.

A case-by-case review will be conducted for students who are already enrolled at USC and may be connected to the scheme. USC will "make informed, appropriate decisions once those reviews have been completed. Some of these individuals may have been minors at the time of their application process," he said.

Stanford University has fired head sailing coach John Vandemoer, who pleaded guilty Tuesday to racketeering conspiracy.

Wake Forest University said it's put head volleyball coach Bill Ferguson on leave. Ferguson faces a charge of conspiracy to commit racketeering.

The University of Texas at Austin said Wednesday it dismissed men's tennis coach Michael Center a day after placing him on leave. Center is charged with conspiracy to commit mail fraud and honest services mail fraud. He could not be reached Tuesday.

Georgetown University said it was "deeply disappointed" to learn former tennis coach Gordon Ernst is charged in the scheme but said Ernst "has not coached our tennis team since Dec. 2017, following an internal investigation that found he had violated University rules concerning admissions."

Yale University said it will continue cooperating with investigators after former women's soccer coach Rudolph "Rudy" Meredith was charged.

UCLA has put men's soccer head coach Jorge Salcedo on leave as he faces a charge of conspiracy to commit racketeering.

"UCLA is not aware of any current student-athletes who are under suspicion," the university said in a statement.

What don't we know?

We don't know whether more people are involved in this scandal, or whether more charges will be filed.

"I will say that the investigation remains active," prosecutor Lelling said. "These are not the only parents involved. We suspect these probably aren't the only coaches involved, and so we will be moving ahead to look for additional targets."

It's also not clear whether any of the students in this scandal will face charges.

"We're still considering that," Lelling said. "The parents, the other defendants, are clearly the prime movers of this fraud. It remains to be seen whether we charge any of the students."