Here's what the code could look like if you wanted to generate a GUID using random bytes from the frameworks's cryptograpically strong RNG.

using System;
using System.Security.Cryptography;

namespace SecureGuidDemo
{
    public class SecureGuid
    {
        public static Guid NewGuid()
        {
            byte[] bytes = {
                 0x00, 0x00, 0x00, 0x00,
                 0x00, 0x00, 0x00, 0x00,
                 0x00, 0x00, 0x00, 0x00,
                 0x00, 0x00, 0x00, 0x00
            };

            using (var rng = new RNGCryptoServiceProvider())
            {
                rng.GetBytes(bytes);
            }

            var time = BitConverter.ToUInt32(bytes, 0);
            var time_mid = BitConverter.ToUInt16(bytes, 4);
            var time_hi_and_ver = BitConverter.ToUInt16(bytes, 6);

            time_hi_and_ver = (ushort)((time_hi_and_ver | 0x4000) & 0x4FFF);

            bytes[8] = (byte)((bytes[8] | 0x80) & 0xBF);

            return new Guid(time, time_mid, time_hi_and_ver,
                bytes[8],  bytes[9],  bytes[10], bytes[11],
                bytes[12], bytes[13], bytes[14], bytes[15]
            );
        }
    }
}