Credit default swaps are also used to structure synthetic collateralized debt obligations (CDOs). Instead of owning bonds or loans, a synthetic CDO gets credit exposure to a portfolio of fixed income assets without owning those assets through the use of CDS. CDOs are viewed as complex and opaque financial instruments. An example of a synthetic CDO is Abacus 2007-AC1, which is the subject of the civil suit for fraud brought by the SEC against Goldman Sachs in April 2010. Abacus is a synthetic CDO consisting of credit default swaps referencing a variety of mortgage-backed securities.