Difference between Server and Data Source in SQL Server Connection String

<add name="ABCD" connectionString="Server=.; Database=XYZ; Integrated Security=true" providerName="System.Data.SqlClient"/>

and

<add name="ABCD1" connectionString="Data Source=.; Initial Catalog=XYZ; Integrated Security=True" providerName="System.Data.SqlClient"/>

Which one is good and secure ? if not secure then how to make them secure ?

NOTE : the application which i am creating is not yet deployed to server , it is only used in my development pc on IIS8 at Localhost