What are long term implications of working with a fake SSN?

Karen writes, "I am in the process of applying for Deferred Action. I am currently using a fake Social Security number that I made up to work at a small retail store.  I had to do what I had to do like many other immigrants. My question is, will USCIS find out that I was or am employed under a false Social Security number?"

USCIS using Don't Ask Don't Tell for using false papers to work:  First of all, USCIS does not require you to list a SSN that was not issued to you.  So right now, even for you, there will be no problem getting approved as long as you meet all the requirements and provide a completed application with all the evidence.

US Government has the means and technology to catch identity theft:  The second issue that you raise is whether the US government can find out what you did at a later stage.  As you are well aware, depending on the specifics of each case, using a false SSN and working without authorization in the US are both serious federal crimes and can often result in denial of immigration benefits (even retroactively), like adjustment of status and naturalization.  Obviously a lot depends on what your employer did with your information.  If they followed the law and provided that information to government agencies then that information has propagated through various databases and will probably stay there forever.  Also, if you filed taxes with that number using your real name and address, you have created a huge paper trail in the system.  In any case, with technologies available today, it is safe to assume that the government can find out almost everything about us if it wants to, often with just a few clicks.  And finally, by law you are required to tell the truth and admit to disclosing how you had income and what you did.

No guidance on negative implications of working without authorization:  At this time the US Government has only announced that using a false SSN is not a barrier to deferral of deportation but it is not an immunity from future prosecution and/or denial of adjustment of status under DREAM Act or after marriage to a US citizen (good moral conduct is a very important condition for naturalization and this may pose problems if you were to ever consider becoming a US citizen).  Having said that, Congress may write laws in the future in such a way that this can be forgiven because so many illegal immigrants are doing it, but at this point no one knows what will happen.