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A CSC (Card Security Code) is a three- or four-digit number printed on your credit card that serves as a security feature to verify you have physical possession of the card. It's one of several names for the same thing—you may also hear it called a CVV, CVC, or CID, depending on which card network or issuer you're using.
Understanding what this code is, how it works, and why it matters helps you protect yourself during online and phone transactions.
The CSC exists to prevent fraudulent charges when you can't swipe or insert your physical card. When you make an online purchase or pay over the phone, you can't hand the card to the merchant. The CSC bridges that gap by confirming that you—or someone with access to the physical card—are authorizing the transaction.
Here's the key security principle: the CSC is not stored on the magnetic stripe or chip of your card. That's intentional. A thief who steals your card number alone cannot complete a transaction online without also having the card in hand to read the code.
For Visa, Mastercard, and Discover cards: The three-digit code appears on the back of the card, to the right of the signature panel.
For American Express: The four-digit code appears on the front of the card, above your account number on the right side.
The exact location varies slightly by card issuer, but these are the standard positions.
Your card has multiple layers of security. It's helpful to understand how the CSC fits into the broader picture:
| Feature | Purpose | Where It's Used |
|---|---|---|
| CSC/CVV | Proves physical card possession | Online and phone transactions |
| Chip | Encrypts in-person transactions | In-store payments (point-of-sale) |
| Magnetic stripe | Stores card data | Older in-store readers; less secure |
| Cardholder name | Basic identity verification | All transactions |
| Expiration date | Confirms card validity | All transactions |
The CSC complements these other features—it doesn't replace them.
Because the CSC is meant to verify you have the physical card, you should treat it like cash. Don't share it in emails, texts, or with unsecured websites. Legitimate merchants will never ask for your CSC over the phone or email—they'll ask for it only when you're entering it yourself during an online checkout or payment.
If someone has your full card number, expiration date, and CSC, they can make online purchases without needing the physical card.
While the CSC adds a meaningful layer of security, it's not foolproof. It protects against certain fraud scenarios (like a stolen card number used online) but doesn't prevent all fraud. Card networks and issuers also use fraud detection algorithms, transaction monitoring, and dispute resolution processes to catch and reverse unauthorized charges.
The CSC alone cannot prevent breaches where merchants store your full card data insecurely, nor can it stop someone who physically steals your card.
When you enter your CSC during an online transaction, the merchant's payment processor verifies that the code matches the card number and expiration date you've provided. If it doesn't match, the transaction is declined. This verification happens in real time but doesn't require the merchant to store the CSC—in fact, legitimate processors are designed not to store it.
Your situation and how you manage your cards will determine how frequently you need to provide this code and how much risk you're exposed to. Protecting it is a straightforward step in keeping your card safe.
