WorldCom Investors Settle    A federal judge approved a \$2.575 billion settlement of a class-action lawsuit by WorldCom investors who claimed they were defrauded by Citigroup, the second-largest settlement ever in a securities fraud case. When the tentative pact was announced by Citigroup in May, it was for \$2.65 billion, but the agreement presented to the judge was reduced by \$75 million. Investors accused Citigroup of hiding WorldCom's financial risks when it helped sell \$10 billion of WorldCom debt in 2001.