Undocumented immigrants can get a credit score by building credit from scratch. One way to do so is through a secured credit card. With a secured credit card, you deposit a certain amount and a line of credit is attached to that number. Make sure you ask if the bank will report your good habits with the secured card to the credit bureaus. If you use the card wisely, usually the bank will offer a way to turn it into a regular credit card. Over time, using the card will build your credit history, thus generating a credit score.