If you use your credit card or debit card online you have probably been asked if you want to register your card with Verified by Visa. It usually comes up after you have entered your card information but before you confirm your purchase. A lot of people are not familiar with exactly what this service does.
If you sign your card up with Verified by Visa you will be asked to enter a password when you shop with a retailer who also uses the Verified by Visa system. If your card is ever stolen the thief will need to know your password to use the card online, but only if they try to shop at those specific retailers.
It’s great in theory, but in practice it’s just another password to remember and it doesn’t provide you with any extra security. If your card gets stolen you are already not responsible for any charges. It’s the company that is receiving the protection here, not the consumer. I wouldn't bother with this service.