ForbiddenWords.cs

using System;

public class ForbiddenWords
{
    public static void Main()
    {
        string textInput = Console.ReadLine();
        string[] forbidenWords = "PHP, CLR, Microsoft".Split(',');
        for (int i = 0; i < forbidenWords.Length; i++)
        {
            forbidenWords[i] = forbidenWords[i].Trim();
            textInput = textInput.Replace(forbidenWords[i], new string('*', forbidenWords[i].Length));
        }

        Console.WriteLine(textInput);
    }
}