One of the many timesaving features that Mac OS X has is the ability to save user names and passwords to a system-wide password management system. You can access this via the Keychain Access application. Web browsers, e-mail clients, FTP programs and other Web functions can all save and retrieve information from the Keychain. There are circumstances, however, when you may not want login information stored in the Keychain. Follow these simple steps to prevent Safari from storing such information.
Open Safari and select Preferences > Autofill.
Uncheck "Autofill web forms: User names and passwords." Safari will no longer attempt to save any new login information.
Click the "Edit" button in the Autofill preferences next to "Autofill web forms: User names and passwords." A sheet window will open listing all the currently saved user names and passwords. Click "Remove All" to ensure that all existing login information is deleted.
Click "Done" and close your Preferences.