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How-To Disallow Saving Usernames/Passwords in Safari
If you’re using a web browser on a public computer, be sure that auto-fill is off for usernames and passwords. A skanky web site cafe might leave this option on, or a user might even deliberately turn it on, then come back later to see what s/he can “harvest”. A reputable service will have configured the computer to reset after ever user, but don’t count on it.
For Apple Safari it’s in the preferences; other browsers have similar settings.