XKCD: Password Strength
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Mozilla Privacy Basics"Learn how to safeguard your privacy online and develop an awareness of how companies and governments track and collect your data online."
Password Protection Services
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LastpassOne of the most popular password manager services available now. This service helps you to generate unique passwords for each account, and then securely stores them. You can install a browser extension to quickly reach them.
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1PasswordA popular password encryption service. Includes apps and web browser extensions for Chrome, Safari, Firefox, Opera, and Microsoft Edge.
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KeePassXA cross-platform password manager.
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Wikipedia's Comparative List of Password ManagersList of notable password managers currently available, including information about licenses, browser and OS support, and delivery format.
Test Your Password Strength
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How Secure is Your Password?Test the strength of your passwords at this site. It will tell you how long it would take a computer to crack your password using conventional methods.
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List of Most Common Passwords (Wikipedia)Wikipedia keeps an updated list of the most common passwords. Check this list to make sure none of your passwords are anywhere close to these!