Computer Associates International Inc. shares plunged nearly 20 percent on Wednesday after reports that the U.S. Attorney's office was investigating the software maker's accounting practices. 

Shares of Islandia, New York-based Computer Associates, the world's No. 4 software maker, were off $3.91, or 15.5 percent, to $21.39 in morning trading on the New York Stock Exchange, where it was the second-most active issue and among the biggest percentage losers. 

Earlier in the morning, the stock had fallen as low as $20.25 -- a level not seen since Jan. 2001. 

On Wednesday, Newsday reported the FBI and the U.S. Attorney's office in Brooklyn, have launched a preliminary investigation of whether the company's accounting practices violated federal criminal fraud laws. 

The newspaper said investigators are focusing on whether the company properly reported its software sales from revenue from services -- fees collected for training, upgrades, and maintenance of its software. 

The article said that its sources stressed that the investigation was in its early stages and that there was no firm evidence that the company did anything illegal. 

Executive Assistant U.S. Attorney William Muller said his department does not comment on investigations. 

Computer Associates said it stood by its accounting practices. 

"We have not been contacted by the authorities regarding any investigation and do not know what, if anything, is being investigated," the statement said. "The reporting of our financial results has always been in accordance with all applicable accounting principles. 

"If there are questions, we look forward to being contacted and to having the opportunity to defend against hearsay and what we believe will prove to be unwarranted concerns." 

Computer Associates has come under attack since it changed its accounting method from a license model, in which the total value of a software sale is booked when the contract is signed, to one that spreads the value over the lifetime of the contract. 

In its quarterly results, the company has issued its financial results on a pro forma basis -- calculating the past earnings as if they had been recorded under the new accounting method. 

Critics -- and even some supporters of the accounting changes -- have said that only the company knows how the results were calculated because the company does not disclose the individual values of the contracts.