how can i get modified words between two strings in asp.net

Question

In my web application, i have two strings and i need to display modified words and count between them.For example

string s1="When you are writing server code you can never be sure what the IP address you see is refereeing to.In fact some users like it this way.";

string s2="When you are wrting server code yu cannn never be sure what the IP address you see is refering to.In fact some users like it this way";

the result is, modified words : wrting,yu ,cannn ,refering

modified words count :4

how to do this can anyone tell me.

Thank you