What is this PUK code for? – Explanation:

Personal Unblocking Key or PUK is one of your ON-LINE CARD ™ secret attributes, perhaps even the most secret one! Along with the ‘Card File’ it gives access to your personal data for modification and helps you to unblock the card in case it was blocked or to claim a replacement card after the expiration date. Please be most cautious about how you handle PUK after it has been issued to you, never store it in data files on your computer, keep it in a hard copy form!

See, how to use PUK for unblocking your card in "How do I ‘unblock’ my ON-LINE CARD ™ ?" section.