A CPN, or Credit Privacy Number, is a nine-digit identification number that can be used instead of a Social Security Number when filling out applications for credit, lease, or any other purchase that requires a credit check. People use CPNs while applying for an apartment for privacy concerns or to avoid scrutiny for financial blemishes on their records, such as a bankruptcy or foreclosure. However, using a CPN deceptively or in place of a Social Security Number is illegal and can even lead to jail time. Applying for an apartment with a CPN can be tricky as not every landlord will accept it due to its association with attempts to conceal poor credit or rental histories.