The ProfileMigrateEventArgs.AnonymousID property contains the unique identifier for an anonymous user. When someone who has been using your application anonymously logs in, you can handle the ProfileModule.MigrateAnonymous event to copy profile property values from the user's anonymous profile to his or her authenticated profile.

When an application that has the user profile enabled is started, ASP.NET creates a new class of type ProfileCommon, which inherits from the System.Web.Profile.ProfileBase class and includes profile properties specified in the Web.config file. When the ProfileCommon class is generated, a GetProfile method is added that enables you to retrieve a ProfileCommon object based on a user name. You can use the GetProfile method of the current profile to retrieve the property values of the anonymous profile. The anonymous property values can then be copied to the current profile for the authenticated user. See the second code example for an example of copying anonymous property values.