The autocomplete features in Safari, IE, Firefox, or Chrome are vulnerable to ID theft and other attacks.

Insecurity expert Jeremiah Grossman is expected to tell a Black Hat conference that the four major browsers have critical weaknesses that have yet to be addressed by their respective companies, and could expose users' passwords, e-mail addresses, and more to attackers.

Grossman will show off a proof-of-concept attack at next week's conference but said that he is only doing so because he could not get the four main software outfits involved to take his hack seriously. If you have autocomplete turned on in many browsers, you just have to begin typing a letter or two in one of the fields before they all fill in with your name and address, possibly your credit card number, and more.

Grossman says attackers can simply create a page with hidden form fields that use JavaScript to enter letters and numbers into each field until it finds one that's a hit, and the browser autocompletes it. All users have to do is load the page, and they likely wouldn't even be aware of what's happening.

The autocomplete exploit works in the two most recent versions of Safari (4 and 5), as well as IE 6 and 7. Firefox and Chrome aren't susceptible to this particular attack, though they were vulnerable to another one involving the autocomplete.

Grossman says that the two browsers can expose stored usernames and passwords for saved sites, making it possible for a cross-site scripting vulnerability to grab the info when a user logs into a Google account or Facebook, for example. He said that he would never have talked about this publicly if Apple had taken this seriously, when he sent a follow-up query.