The expansion of household debt was financed with mortgage-backed securities (MBS) and collateralized debt obligations (CDO), which initially offered attractive rates of return due to the higher interest rates on the mortgages; however, the lower credit quality ultimately caused massive defaults. While elements of the crisis first became more visible during 2007, several major financial institutions collapsed in September 2008, with significant disruption in the flow of credit to businesses and consumers and the onset of a severe global recession.