Many undocumented immigrants pay income and social security taxes in the hope that doing so will assist them in someday gaining citizenship. Many use an ITIN to file, many use a fake SSN and some use a stolen SSN. Before getting upset about the "stolen" part, remember that someone is using another's SSN to pay *into* the system - so in reality someone may end up having much more credit in his or her social security account than he or she actually contributed. All of the unidentified money from undocumented immigrants and their employers - and it's a huge amount - is used by the government to pay out benefits to those who are in social security. So... They're paying into the system and should get the same deductions as everyone else.