A computer-implemented service integrates with merchant sites to enable registered users of the service to perform purchase transactions on the merchant sites. In one embodiment, a merchant can incorporate a reference to a display object served by the service into coding of a page of the merchant's site. When the page is loaded by a user's browser, the reference causes the browser to request the display object from the service for display on the page. If the user is recognized by the service, the service may return a personalized display object that includes functionality for the user to perform a purchase transaction using the service. Also disclosed are embodiments that enable users to initiate transfers of personal account information to the merchant sites.