using System;

using System.Text.RegularExpressions;

var regex = new Regex(@"(https?://\S*[^\W])");

​

var original = "Lorem http://www.example.com. https://www.example.com";

var parsed = regex.Replace(original, "<a href=\"$1\">$1</a>");

​

Console.WriteLine("Original: " + original);

Console.WriteLine("Parsed:   " + parsed);