That's good information. Do you have any special security integrated into your web services architecture, such as an authentication technique? Do you make calls to Web Services over an "https" connection?
I've been reading about proposed standards (i.e. Microsoft/IBM "WS-Security") but haven't seen any real examples. The WS-Security involves a kind of authentication for users of the web service, who are then issued an identifying token that's passed in with subsequent SOAP headers to identify the user of the Web Service.
Depending on what type of security you're wanting you can either authentic the user which is part of the MM.NET Framework or encrypt the data being transmitted which would require an SSL Certificate like from Verisign. There are cheaper SSL Certificate alternatives out there - just search Google for SSL Provider.
Verisign has a Free Guide on their homepage - good luck!
