I have been asked to create a web service that communicates with Auth.NET CIM and Shipsurance API.  My web service will be used by multiple applications (one a desktop and another a web application). I am confused whether I should build a WCF or an asmx web service. Auth.NET CIM and Shipsurance API have asmx web services which I would be calling in my newly created web service. So is WCF the right approach or can I stay with asmx? 
WCF or ASMX WebService
c#;.net;web services;wcf
You can go for WCF. If you read the differences between wcf and webservices you may understand the necessity of wcf over webservices. WCF offers duplex communication with bindings and improved security. you can configure your data transfer mode and security. I suggest you to read WCF Bidnings.First of all, wcf is webservice. you can either create a WCF Project library(creates a *.dll) or WCF service application (Appication that you can host).You can communicate with WCF to a old webservices. WCF has better features and security which you may want to consider before going to web services