The autocomplete attribute in a form typically has two effects.
if you read Turning off form autocompletion
it stops the browser saving field data for later autocompletion on similar forms though heuristics that vary by browser.
it stops the browser caching form data in session history. When form data is cached in session history, the information the user has filled in will be visible after the user has submitted the form and clicked on the Back button to go back to the original form page.
So if you've saved the username/password login information in your browser by choosing to remember the login for that site you likely will still see them autofilled by your browser.
Check out this how to remove saved passwords from a web browser/
or if you can use Jquery simply include the jQuery library and a jQuery script with the following code:
you should read this:
Turning off form autocompletion - mozilla
$(document).ready(function() {
$(":input").attr("autocomplete","off");
});