There is a new class, System.Security.SecureString . To understand the purpose of this class, think about eg. a password. You probably never want anyone to see the password, but if you store it in a simple System.String instance there are some security risks. For example, how do you get rid of the value when you've finished with the string? You can set the reference to the string to null , but the value itself is still in the managed heap. Indeed there may be several copies of it lurking around if the garbage collector has moved it during previous collections. Bluntly, the heap was never designed to guard against someone going through it with a memory dump tool. SecureString solves this kind of issue.
Assigning a value to secure string is pretty simple and just like assigning a value to a string, eg:
System.Security.SecureString pword = new System.Security.SecureString();
pword = "admin";
pword.Clear();
The value is stored in an encrypted form, and SecureString also has a Clear() method that completely wipes out the data. Extracting the value from a secure string is possible but complicated - and not often done.