Internet Explorer 7 can store your previous entries in the Web address bar (site URL's) and for online forms (i.e. addresses and passwords). This was a good idea in another time and place but not anymore. It's a very unsafe thing to do. Having Internet Explorer 7 save passwords and user names for Web forms means that anyone who uses your computer will have access to any sites that you need a password or username for; this means that if you do online banking or make online purchases, anyone who has access to your computer will have access to those sites. Not good! This is like leaving the key to your house under your doormat, or leaving the keys to your car on the dashboard. Don't do it. We recommend you use a program like RoboForm where only you can access your passwords and usernames. But whatever you use we recommend you don't use your browser to store passwords and user IDs.

How To Turn Off AutoComplete
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• In Internet Explorer, on the Tools menu, click Internet Options.
• Click the Content tab.
• Next to "AutoComplete" click the "Settings" button
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• Remove the check marks next to "Forms" and "User names and passwords" on forms.
• See picture below:
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• Click OK

How To Delete Saved AutoComplete Form Data
• In Internet Explorer 7, click Tools then click Internet Options.
• Click the "General" Tab
• Under "Browsing History" click the "Delete" Button
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• Next to "Form data" click the "Delete forms" button
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• Click "Delete Passwords" Button
• Or if you don't want to save your browsing History, Cookies or Temporary Internet Files, you can get rid of everything at once by clicking the "Delete All" button.

Sources:
• CloudEight