[jaxomlotus]

Another method would be to show a user a list of all fields that are about to be filled in as part of the autocomplete prompt. This isn't very scalable for massive forms, but should be enough of an alert to a user that something is amiss on screen to make up for those cases.

[ycmbntrthrwaway]

You can scale it by classifying fields into groups. Then user can decide gradually if he wants to share his name. Later, application may ask for location (browsers can already do this), employer info, contact data etc.

What is needed is integration with permission granting mechanisms, which already exist in browsers.

[itissid]

Actually this problem looks is a lot like how Android App permissions are managed. Not long ago some apps used to ask you at install time that they want access to your google email, contacts, wifi and so on. A better app permission model (which I think is now in android) is to ask these "lazily" as the app needs them and let the user decide at that point.

[ehsankia]

I like this best too. All it does is add one more click (when you select the auto fill info, it pops up with all the data and you just approve) and it also solves a lot of wrong fills that can happen.

There's often sites that are poorly coded, and autofills ends up putting my phone number in some random field and I have to manually delete it.

[kalleboo]

Safari does this already