In the early 2000s, the world's top accounting firms were known as the "Big 5": Deloitte, PwC, EY, KPMG, and Arthur Andersen. But everything changed after the infamous Enron scandal.

Enron, a Texas-based energy company, was once celebrated for innovation in energy trading. However, in 2001, it was revealed that Enron had been hiding billions in debt using complex structures called Special Purpose Entities (SPEs).

These accounting tricks made the company appear far more profitable than it actually was.

Shockingly, Enron's auditor was Arthur Andersen, which not only missed the fraud but was later caught shredding crucial audit documents during the investigation. This obstruction of justice raised serious ethical concerns.

In December 2001, Enron filed for bankruptcy, and by 2002, Arthur Andersen was convicted, and its license to audit public companies was revoked. The fallout was massive - over 85,000 employees were affected, and the Big 5 became the Big 4.

Though Andersen's conviction was later overturned, the damage was irreversible. Had the scandal not occurred, Arthur Andersen might still be a dominant force in global accounting today.