The Mystery of Your Name Being Filled In Automatically
When you click on a web form, your name, email address, and home address automatically appear as suggestions. It's convenient, but have you ever wondered "how does my browser know my name?"
How Autofill Works - Three Sources
Your browser's autofill feature pulls data from three sources.
1. Past Input History
When you enter your name or email address in a form, the browser remembers it. The next time it encounters a similar form, it displays your past entries as suggestions. It uses the form field names (name attributes) as clues to determine "this is a name field" or "this is an email field."
2. Saved Browser Profiles
Chrome, Safari, and Firefox have "autofill settings" where you can pre-register your name, address, phone number, and credit card information. Registered information is automatically displayed as suggestions in matching forms.
3. Password Managers
Built-in browser password managers or external tools like 1Password and Bitwarden store login credentials for each site. They recognize URLs and autofill the corresponding username and password. For tips on creating strong, unique passwords that these managers can store, see our password security guide.
Security Risks of Autofill
While convenient, autofill carries security risks.
Hidden Form Attacks
Malicious websites can place hidden forms (forms made invisible with CSS) to exploit the browser's autofill feature and steal personal information. Even if you think you only entered your email address in the visible form, your name, address, and phone number may have been autofilled into hidden fields. This technique is often used alongside phishing attacks, making it doubly important to verify the sites you visit.
Current major browsers have been improved to not autofill hidden forms as a countermeasure. However, older browsers remain vulnerable.
Information Leaks on Shared Devices
On computers shared with family or colleagues, information saved in autofill could be seen by others. On shared devices, it's recommended to use separate browser profiles or disable autofill. If you suspect your saved credentials have been exposed, follow the steps in our data breach response guide to secure your accounts.
How to Manage Autofill
- Chrome: Settings → Autofill and passwords → Manage addresses and payment methods
- Safari: Settings → AutoFill → Manage contact info and credit cards
- Firefox: Settings → Privacy & Security → Forms and Autofill
Periodically delete unnecessary information and use credit card autofill with caution.
Summary
Browser autofill pulls information from three sources: past input history, saved profiles, and password managers. While convenient, there are risks from hidden form attacks and information leaks on shared devices. On sites like IP Check-san that don't require form input, you don't need to worry about autofill risks.