Allstate (ALL) sued Credit Suisse (CS) for failing to disclose the toxic nature of the underlying loans within $231 million of  mortgage-backed securities the insurer purchased. The insurance giant claims Credit Suisse knew the residential mortgages behind the securities were risky, but failed to disclose the information to investors. In its complaint, Allstate accuses the financial institution of fraud, fraudulent inducement and negligent misrepresentation. At one point, Allstate says 21% of the loans originated in one series of securities were originated by subprime lender Countrywide Financial, which was acquired by Bank of America (BAC) in 2008 after the subprime market meltdown. Allstate also cites data from mortgage insurer MBIA Insurance (MBI) in its lawsuit, saying "MBIA's findings demonstrate that the essential characteristics of the mortgage loans underlying the certificates sold to Allstate were misrepresented, and that the problems in the defendants’ underwriting practices were systemic." It's the second time in two weeks, the insurer has gone after sellers of mortgage-backed securities. Allstate also sued JPMorgan Chase (JPM) and subsidiaries Bear Stearns and Washington Mutual for fraudulently selling the insurer more than $750 million in residential mortgage-backed securities backed by toxic loans. Write to Kerri Panchuk.