What is the U.S. government looking for when delving into the background of those who wish to reside in the U.S. either on a temporary or permanent basis? Here’s the fact sheet from the U.S. Citizenship and Immigration Service (USCIS) on the matter:
All applicants for a U.S. immigration benefit are subject to criminal and national security background checks to ensure they are eligible for that benefit. USCIS, the federal agency that oversees immigration benefits, performs checks on every applicant, regardless of ethnicity, national origin or religion.  
Since 2002, USCIS has increased the number and scope of relevant background checks, processing millions of security checks without incident.  
USCIS is responsible for ensuring that our immigration system is not used as a vehicle to harm our nation or its citizens by screening out people who seek immigration benefits improperly or fraudulently. These security checks have yielded information about applicants involved in violent crimes, sex crimes, crimes against children, drug trafficking and individuals with known links to terrorism. 
These investigations require time, resources, and patience and USCIS recognizes that the process is slower for some customers than they would like. Because of that, USCIS is working closely with the FBI and other agencies to speed the background check process. 
USCIS normally uses the following three background check mechanisms but maintains the authority to conduct other background investigations as necessary:  
*The Interagency Border Inspection System (IBIS) Name Check: IBIS is a multi-agency effort with a central system that combines information from multiple agencies, databases and system interfaces to compile data relating to national security risks, public safety issues and other law enforcement concerns. 
USCIS can quickly check information from these multiple government agencies to determine if the information in the system affects the adjudication of the case. 
Results of an IBIS check are usually available immediately.
FBI Fingerprint Check:
The FBI fingerprint check provides information relating to criminal background within the U.S. Generally, the FBI forwards responses to USCIS within 24-48 hours. If there is a record match, the FBI forwards an electronic copy of the criminal history to USCIS. At that point, a USCIS adjudicator reviews the information to determine what affect it may have on eligibility for the benefit. 
Although the vast majority of inquiries yield no record or match, about 10% do uncover criminal history (including immigration violations). In cases involving arrests or charges without disposition, USCIS requires the applicant to provide court certified evidence of the disposition. Customers with prior arrests should provide complete information and certified disposition records at the time of filing to avoid adjudication delays or denial resulting from misrepresentation about criminal history. Even expunged or vacated convictions must be reported for immigration purposes.
FBI Name Checks:
The records maintained in the FBI name check process consist of administrative, applicant, criminal, personnel and other files compiled by law enforcement. 
Initial responses to this check generally take about two weeks. In about 80% of the cases, no match is found. Of the remaining 20%, most are resolved within six months. Less than 1% of cases subject to an FBI name check remain pending longer than six months.  
For most applicants, the process outlined above allows USCIS to quickly determine if there are criminal or security related issues in the applicant’s background that affect eligibility for immigration benefits. Most cases proceed forward without incident.