SAY you’ve come across a discount online retailer promising a steal on hand-stitched espadrilles for spring. You start setting up an account by offering your e-mail address — but before you can finish, there’s a ping on your phone. A text message. You read it and respond, then return to the Web site, enter your birth date, click “F” for female, agree to the company’s terms of service and carry on browsing.
