If your credit card offers a personal identification number (PIN), it’s for your protection. While signatures can be forged, having a PIN attached to a credit card means someone needs to know your “secret code” in order to use it for certain kinds of purchases. Do you protect your PIN?

There are certain situations where it’s a good idea to change your PIN. How often do you do it? For most people the answer is probably “not enough.” Here are three scenarios where you should definitely change your credit card’s PIN:

1. You’re still using the original PIN the credit card company gave you.

It’s always a good idea to change your PIN from the default number the bank gives you to a number that you’re more likely to remember. Most banks even recommend this to their credit and debit card customers.

When you choose a PIN that you’re likely to remember (but something others still won’t be able to guess easily), you have no need to write it down. Writing down your PIN so you can refer to it when using your credit card is one of the biggest mistakes that you can make. It means your credit card and PIN (which is supposed to be a security feature) might both be readily available to a thief if your card is stolen.

2. Someone else saw you enter your PIN (or you gave it to someone).

Just because you trust someone with your PIN one day, it doesn’t mean they should be trusted to have access to your credit card accounts all the time. If you gave it to someone, it’s a good idea to change it.

It’s an even better idea to change your PIN if you even suspect that an unauthorised person saw you enter your PIN somewhere (like an ATM for a cash advance).

3. You’re using the same PIN on other credit cards or debit cards.

It’s tempting to use the same PIN for all of your cards. That way you only have to remember one number when you use an ATM or make a PIN point-of-sale purchase. This isn’t a good idea though.

If all of your credit cards use the same PIN, then a thief only needs to know one number to access all of your cards. For example, let’s say you’re travelling on holiday. Someone watches you enter your PIN for your St. George Visa debit card at an ATM. You put your card back into your wallet. The thief then steals your wallet.

If you use that PIN for all of your cards, not only will they have access to your bank balance through your debit card, but they’ll also be able to take out cash advances on your credit cards, leaving you broke (or at least far worse off than you would have been if you took the safer approach of having a different PIN for each card).

Remember that a PIN isn’t a cure-all for your security woes. They’re only true credit card security features if you treat them that way and protect them from others. Your PIN should be for your eyes only — well, you and your authorised additional cardholders at least.