To prosecute or not to prosecute?
Check it out:

If federal law enforcement officers apprehended a person who had been using a false Social Security Number, a federal prosecutor with a heavy caseload dominated by more serious crimes might decide not to indict the person. Whatever its merits, that would be an act of prosecutorial discretion.

But what if the prosecutor were to tell this user of a false Social Security Number: It is okay for you to continue using that false Social Security Number tomorrow. In fact, you may do so with impunity for the next three years.