The personal touch
If you see the MasterCard SecureCode logo, it indicates a participating merchant, even if you don't, they may still offer the protection. There's no need to log in to your account, the store/retailer will automatically recognise your MasterCard card number during the transaction. Then you'll be given an identifiable Personal Greeting. This is an assurance that you're genuinely communicating with your card issuer, but if you don't get this or it seems incorrect, don't enter your MasterCard SecureCode. Instead, call the phone number on the back of your MasterCard card, to report a possible fraud.
Assuming it's all above board, review the purchase details are correct and then you'll be prompted to enter your SecureCode. Everything will be completed and you can be safe in the knowledge that your details are protected.
MasterCard SecureCode is just one security measure that credit card providers are adopting. Others may use similar methods to verify your identity. Entering a code may be a minor inconvenience, but in an age when identity theft is rife, it's a necessary one. It ultimately means complete peace-of-mind when shopping online.