The mortgage-backed securities dealt with till now are agency mortgage backed securities. There are other MBS which can be for any kind of real estate property. For non-agency backed securities, the first lien is on the mortgaged property. The non-agency backed securities can take the form of pass-throughs or CMOs. In this market, the CMOs are created either from a pool of pass-throughs or unsecuritized mortgage loans. The main difference between an agency mortgage backed-security and a non-agency mortgage backed-security is that the latter does not carry precise government guarantee of payment of interest and principal as is with an agency security.