It refers either from the <membership> configuration section
<membership defaultProvider="SqlMembershipProvider" > <providers> <clear/> <add name="MySqlMembershipProvider" connectionStringName="LocalSQLServer" applicationName="MyAppName" type="System.Web.Security.SqlMembershipProvider, System.Web, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" /> </providers> </membership>
or from the place where you initialize the SqlMembershipProvider in your code.
As far as I can see, there is no default - you (or the code you copied) should have named it that way.
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