I stumbled on this today, original location is below. - Robert Porter 

SecureString Class

Represents text that should be kept confidential. The text is encrypted for privacy when being used, and deleted from computer memory when no longer needed. This class cannot be inherited.

Namespace: System.Security
Assembly: mscorlib (in mscorlib.dll)

http://msdn2.microsoft.com/en-us/library/system.security.securestring.aspx

Source: Use SecureString in .NET 2.0 for Confidential Text
Originally published on Fri, 01 Dec 2006 21:28:00 GMT by Devin A. Rychetnik