Whatever you type in your browser (search terms, usernames etc) gets stored with windows and its used as Auto Complete feature of browser. As the data is displayed, its a serious threat to PC users privacy. Very easily, all your activities can be identified by just pressing down key in a text box.

Even deleting these values using browser option does not completely wipe off the data. Regular usage of Windows Washer is highly advisable to permanently and effectively shred these data from your computer.