At least five firms revealed recently that their non-agency mortgage-backed security activity is under investigation by the Securities and Exchange Commission and/or the Department of Justice. The firms are Ally Financial, Citigroup, Goldman Sachs, JPMorgan Chase and Wells Fargo. The companies revealed little about the topic of the investigations, though some are related to mortgage securitization and disclosures while others relate to potential origination or underwriting fraud ... [Includes four briefs]