What will happen to illegal immigrants stealing identities?

The use of Social Security numbers that do not belong to illegal immigrants is so widespread that many actually have more than one.  Some go as far as to steal the identity of an American citizen or legal resident (it is estimated that as many as 10 million identities are stolen each year, mostly by undocumented aliens).  Fortunately for the undocumented aliens, most of the real owners of these SSN do not find out or not find out right away or it takes some time before the legal process kicks in.  It is important to clarify right away that any abuse of SS# is a crime (to state it in simple terms, using a number that was not assigned to you by the Social Security Administration is a crime and using that number to work is violation of many additional laws).  Even using a completely made up number can put you in trouble later on because if it is assigned to a legal individual, you have broken the law.

Breaking the law related to SSN has consequences:   Simply because most people are never caught or prosecuted (sadly for you, the money goes into the Social Security trust fund that will be eventually distributed only to those legally entitled to receive it), it does not mean that it is okay to do it or that some day you may not get into trouble with the law (what is interesting is that rightful owners or a number are not notified by the SSA that someone is using their number and it is up to them to find that out the hard way and act on it).  Similarly, just because USCIS is not asking DREAMers applying for DACA if they have abused Social Security numbers, it does not mean that they are immune from prosecution at a later time or that they may not be denied an immigration benefit in the future (using someone's SS# is a felony and generally disqualifies an individual from any immigrant benefit). 

Illegal immigrant using false SSN jailed and deported:   That is why I wanted to highlight the case of Candida Gutierrez whose identity was stolen by Mexican national Benita Cardona-Gonzalez who is in the United States illegally.  Like many other unauthorized aliens, she started living a comfortable life as Ms. Gutierrez getting mortgage, credit cards, driver's license, etc.  When the real Ms. Gutierrez started to suffer the consequences of someone abusing her credit history, Benita Cardona-Gonzalez was charged and not only will she spend a year and half in jail she will also be deported to Mexico.  The lighter sentence was given because Benita Cardona-Gonzalez pleaded guilty and struck a deal with the prosecutors.  The evidence against her was so overwhelming that she had no choice.

How does the Government collect evidence on using fake papers?   The fact to remember is that if you have been doing the same, you are accumulating enormous evidence that can and will be used against you.  For example, if you use a stolen SSN to find employment even at a tiny store and fill a forms like I-9, within a matter of days that information is populated in databases of IRS and the treasury department of the state in which your employer is based.  It is also shared with unemployment division in the state and depending on where you are, it can be shared with other databases.  While your employer may not use eVerify for whatever reason, when the IRS detects a mismatch between the name and the number (as many 9 million mismatches happen each year mostly due to the undocumented immigrants using numbers that do not belong to them), it notifies the DHS.  By filing your taxes with the false number, you keep adding to the evidence in the Federal and state records.  Opening bank and credit accounts, joining a school/university, applying for auto loans, etc. are other activities that result in accumulation of solid evidence of fraud.