In a Manhattan court yesterday, Yates pled guilty to one count of conspiracy to commit securities fraud and one count of committing securities fraud.

According to reports in the Boston Globe Yates told the federal court that he was instructed by supervisors to misreport expenses, allowing WorldCom to overstate earnings by $5bn between October 2000 and April 2002.

He is now expected to assist authorities in their case against former chief financial officer Scott Sullivan, who along with Yates pled not guilty in July to charges of conspiring to hide about $7.2bn of operating expenses.

Valued at $175bn (£111bn) at its height in 1999, WorldCom's collapse followed fraud charges after the company admitted hiding $1.2bn in losses by falsely accounting for expenses worth $3.85bn.

It file for Chapter 11 bankruptcy protection in July this year - the biggest ever filing in US corporate history.