Earlier, I explained the importance of checking to see that a web page is protected with SSL before typing any personal information in a form. Crucial as that is, it's not the only factor determining whether your form information is safe. You must also consider how the information is stored and accessed on your Mac.
Most web browsers — and numerous third-party utilities — include facilities for storing usernames, passwords, addresses, account numbers, and other such data commonly used on web forms and then inserting the information for you automatically or on demand. Automatic form-filling features save you typing, reduce the need to remember passwords, and ensure accuracy when typing data. But the flip side of this convenience is that anyone else with physical access can also fill in web forms automatically using your data — thus compromising your security and privacy and possibly your money — unless you take explicit steps to protect this information.
If you're the only person who uses your Mac and if you keep it in a safe place where no one else can access it, you may find that implementing additional security measures is more bother than it's worth. But in shared or public environments or when there's a significant risk of your Mac being stolen, protecting form data is extremely important.
Every browser handles form filling in its own way, but what typically happens when you turn on an AutoFill ...