RandomFileGenerator.cs

using System;
using System.IO;

namespace Generators.RandomStream.Demo
{
    class Program
    {
        static Random _random = new Random();

        static void Main(string[] args)
        {
            string filePathFormat = @"c:\tests\file_{0}_{1}.bin";

            foreach (var f in Directory.EnumerateFiles(Path.GetDirectoryName(string.Format(filePathFormat, 0, 0))))
            {
                File.Delete(f);
            }

            //Generate 0-1mb random file 20 file
            for (int i = 0; i < 20; i++)
            {
                var sizeOfFile = _random.Next(0, 1048576);

                using (var orginal = new FileStream(string.Format(filePathFormat, i, 0), FileMode.OpenOrCreate, FileAccess.Write))
                {
                    for (int j = 0; j < sizeOfFile; j++)
                    {
                        orginal.WriteByte((byte)_random.Next(0, 255));
                    }
                }

                var modifiedFileSize = _random.Next(sizeOfFile / 2, sizeOfFile * 2);

                using (var orginal = new FileStream(string.Format(filePathFormat, i, 0), FileMode.Open, FileAccess.Read))
                {
                    using (var modified = new FileStream(string.Format(filePathFormat, i, 1), FileMode.CreateNew, FileAccess.Write))
                    {
                        var b = 0;
                        var k = 0;

                        while ((--modifiedFileSize) > 0)
                        {
                            b = orginal.ReadByte();

                            if (modifiedFileSize < k)
                                break;

                            var rnd = _random.Next(0, 100);

                            if (rnd % 17 == 0)
                                modified.WriteByte((byte)_random.Next(0, 255));
                            else if (rnd > 80)
                                continue;
                            else
                                modified.WriteByte((byte)b);
                        }


                    }

                }
            }
        }
    }
}