OpenID is an service which allows users to log on to many different web sites using a single username / password. This eliminates the need to create and remember a
strong username / password for each site. The assumption, of course, is you create a strong OpenID.
Of course, if that information is lost or stolen, you're in big trouble.
JanRain is "a recognized leader and primary catalyst driving the OpenID market forward," and they've created a second authentication layer for OpenID, using a callback service.
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Source: Tech-Ex