A Yahoo! Security Key is a security code, similar to the PIN you use at an ATM, designed to protect your most sensitive information. When you try to access certain areas of Yahoo!, you'll be prompted to create or enter this code. If you're a Business Mail owner or administrator, you'll be asked to enter a Security Key when you create a POP-only email user and the associated password.
Note: Verification of your Security Key, as well as the display of your protected sensitive information, is always performed using a secure (SSL) connection. Learn more.