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When you sign into your online accounts – a process we call "authentication" – you're proving to the service that you are who you say you are. Traditionally that's been done with only a username and a password. Unfortunately, that's not a very good way to do itthis method alone is not very secure. Usernames are often easy to discover; sometimes they can be your email address. Since passwords can be hard to remember, people tend to pick simple ones or use the same password at many different sites. This can make an account easy to break into by criminals who want to access the account owner’s information.
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