Class actions alleging securities fraud fell 24% in 2009, as cases related to the credit crunch, and especially subprime-mortgage losses, began to dry up, according to a study released Tuesday.

"That pig has moved through the python," Stanford University Law School professor Joseph Grundfest said of the financial traumas that helped trigger the recession and financial crisis. "All of the major cases that were profitable have already been filed. The pool is in effect fished out."

The number of companies sued on stock-fraud claims dropped to 169 last year, from 223 in 2008, compared with an annual average of 197 cases over the previous decade, according to the study by Stanford Law School's Securities Class Action Clearinghouse and Cornerstone Research.

Nearly half of the decline stems from the lack of new grounds for suits related to credit losses, the researchers found. A drop in stock market volatility also was a factor, the study said.

The companies sued for alleged securities fraud in 2009 on behalf of groups of investors include UBS AG, American Express Co., General Electric Co., Citigroup Inc., Moody's Investors Service Inc., Genzyme Corp., Boeing Co., State Street Corp., Royal Bank of Scotland Group PLC and Chesapeake Energy Corp., according to the Stanford group's Web site. All such cases must be filed in federal court.

Stock-fraud suits hit a record 266 in 2002 after an accounting scandal led Enron Corp. to file what was then the biggest bankruptcy filing in U.S. history. The 2001 collapse of the energy trading company led in part to the passage of the Sarbanes-Oxley Act, which imposed stricter accounting rules.

Filings related to the credit crisis fell from 100 in 2008, to 53 last year. Still, almost half of all the 2009 class actions named financial industry companies as defendants. Cases related to the fraud committed by Bernard L. Madoff and to other alleged Ponzi schemes accounted for 18 filings.

The study found there was a longer delay from the time of the fraud, as alleged in complaints, to the filing of suits. More than 60% of claims with a time lag of more than six months were filed by the firm Coughlin Stoia Geller Rudman & Robbins LLP in San Diego, according to the study.

Securities-fraud suits typically involve claims by investors that companies hid negative information to keep their stock prices artificially high. One or more investors then sue for the loss in share value that follows when the information becomes public.

The plaintiffs usually seek to represent the interests of all company investors in a class action in order to increase their leverage and obtain more favorable settlements.

Fewer class actions may lead to a drop in claims for insurers such as Travelers Cos. and Chubb Corp. that sell coverage for lawsuit costs tied to management errors or negligence, said Mark Dwelle, an analyst at RBC Capital Markets in Richmond, Va.

Directors' and officers' insurers may curb price increases or lower rates next year as a result, Aon Corp., a Chicago insurance brokerage, said in a Dec. 18 statement. Prices paid by financial firms for such insurance rose 3.2% in the three months that ended Sept. 30, after climbing at least 10% in each of the four prior quarters.

"The worst fears were probably overexaggerated around this time a year ago," Dwelle said. "It's taken a while for reality to catch up with the facts. Recall this time a year ago we were concerned that basically every financial institution in America was going to go under."

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