Bankrupt WorldCom says it has uncovered 3.3 billion dollars (£2.15 billion) more in bogus accounting.
The disclosure brings the total of misstated earnings to 7.1 billion US dollars (£4.6 billion).
The telecommunications firm also warned it might find more accounting problems as it continues its investigation.
The restatement comes amid a string of accounting scandals that has tarnished some of the largest firms in the US, felling once-mighty companies such as Enron.
The revelations of corporate malfeasance has severely shaken investor confidence, pummelling stocks and pension funds.
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