Does the USCIS conduct a background check on spouse?

Brian asks, "I am filing my naturalization paperwork based on being a green card holder for 5 years.  I did not receive a family based green card even though my spouse is a native born American.  Why does the government want to know all about my wife, including her SS# and other intimate details about her life?  Will they pull up information about her past as well?"

It is standard for USCIS to seek that information (along with information about children) to make sure that neither of you has engaged in bigamy or polygamy.  It is also generally believed that the Feds want to know if you have criminal or terrorism links through your spouse and family members so by having access to that information they can make sure that none of those people are in their databases.  Chances are that if there is a match, your application will be scrutinized very closely and be prepared for massive delays.  Depending on specifics of the case, your application may even be denied on national security grounds (assuming that your spouse or children are engaged in activities that may fit the profile of a terrorist or someone who is plotting to harm the United States).