Защита процесса от закрытия(убийства) в три шага!

1)Подключаем пространство имен необходимых нам библиотек:

using System.ComponentModel;
using System.Security.AccessControl;
using System.Security.Principal;
using System.Runtime.InteropServices;

2)Вставляем код в код главной формы:

[DllImport("advapi32.dll", SetLastError = true)]
static extern bool GetKernelObjectSecurity(IntPtr Handle, int securityInformation, [Out] byte[] pSecurityDescriptor,
uint nLength, out uint lpnLengthNeeded);

public static RawSecurityDescriptor GetProcessSecurityDescriptor(IntPtr processHandle)
{
    const int DACL_SECURITY_INFORMATION = 0x00000004;
    byte[] psd = new byte[0];
    uint bufSizeNeeded;
    // Call with 0 size to obtain the actual size needed in bufSizeNeeded
    GetKernelObjectSecurity(processHandle, DACL_SECURITY_INFORMATION, psd, 0, out bufSizeNeeded);
    if (bufSizeNeeded < 0 || bufSizeNeeded > short.MaxValue)
        throw new Win32Exception();
    // Allocate the required bytes and obtain the DACL
    if (!GetKernelObjectSecurity(processHandle, DACL_SECURITY_INFORMATION,
    psd = new byte[bufSizeNeeded], bufSizeNeeded, out bufSizeNeeded))
        throw new Win32Exception();
    // Use the RawSecurityDescriptor class from System.Security.AccessControl to parse the bytes:
    return new RawSecurityDescriptor(psd, 0);
}

[DllImport("advapi32.dll", SetLastError = true)]
static extern bool SetKernelObjectSecurity(IntPtr Handle, int securityInformation, [In] byte[] pSecurityDescriptor);

public static void SetProcessSecurityDescriptor(IntPtr processHandle, RawSecurityDescriptor dacl)
{
    const int DACL_SECURITY_INFORMATION = 0x00000004;
    byte[] rawsd = new byte[dacl.BinaryLength];
    dacl.GetBinaryForm(rawsd, 0);
    if (!SetKernelObjectSecurity(processHandle, DACL_SECURITY_INFORMATION, rawsd))
        throw new Win32Exception();
}

[DllImport("kernel32.dll")]
public static extern IntPtr GetCurrentProcess();

[Flags]
public enum ProcessAccessRights
{
    PROCESS_CREATE_PROCESS = 0x0080, //  Required to create a process.
    PROCESS_CREATE_THREAD = 0x0002, //  Required to create a thread.
    PROCESS_DUP_HANDLE = 0x0040, // Required to duplicate a handle using DuplicateHandle.
    PROCESS_QUERY_INFORMATION = 0x0400, //  Required to retrieve certain information about a process, such as its token, exit code, and priority class (see OpenProcessToken, GetExitCodeProcess, GetPriorityClass, and IsProcessInJob).
    PROCESS_QUERY_LIMITED_INFORMATION = 0x1000, //  Required to retrieve certain information about a process (see QueryFullProcessImageName). A handle that has the PROCESS_QUERY_INFORMATION access right is automatically granted PROCESS_QUERY_LIMITED_INFORMATION. Windows Server 2003 and Windows XP/2000:  This access right is not supported.
    PROCESS_SET_INFORMATION = 0x0200, //    Required to set certain information about a process, such as its priority class (see SetPriorityClass).
    PROCESS_SET_QUOTA = 0x0100, //  Required to set memory limits using SetProcessWorkingSetSize.
    PROCESS_SUSPEND_RESUME = 0x0800, // Required to suspend or resume a process.
    PROCESS_TERMINATE = 0x0001, //  Required to terminate a process using TerminateProcess.
    PROCESS_VM_OPERATION = 0x0008, //   Required to perform an operation on the address space of a process (see VirtualProtectEx and WriteProcessMemory).
    PROCESS_VM_READ = 0x0010, //    Required to read memory in a process using ReadProcessMemory.
    PROCESS_VM_WRITE = 0x0020, //   Required to write to memory in a process using WriteProcessMemory.
    DELETE = 0x00010000, // Required to delete the object.
    READ_CONTROL = 0x00020000, //   Required to read information in the security descriptor for the object, not including the information in the SACL. To read or write the SACL, you must request the ACCESS_SYSTEM_SECURITY access right. For more information, see SACL Access Right.
    SYNCHRONIZE = 0x00100000, //    The right to use the object for synchronization. This enables a thread to wait until the object is in the signaled state.
    WRITE_DAC = 0x00040000, //  Required to modify the DACL in the security descriptor for the object.
    WRITE_OWNER = 0x00080000, //    Required to change the owner in the security descriptor for the object.
    STANDARD_RIGHTS_REQUIRED = 0x000f0000,
    PROCESS_ALL_ACCESS = (STANDARD_RIGHTS_REQUIRED | SYNCHRONIZE | 0xFFF),//    All possible access rights for a process object.
}
public void block()
{
    // Get the current process handle
    IntPtr hProcess = GetCurrentProcess();
    // Read the DACL
    var dacl = GetProcessSecurityDescriptor(hProcess);
    // Insert the new ACE
    dacl.DiscretionaryAcl.InsertAce(
    0,
    new CommonAce(
    AceFlags.None,
    AceQualifier.AccessDenied,
    (int)ProcessAccessRights.PROCESS_ALL_ACCESS,
    new SecurityIdentifier(WellKnownSidType.WorldSid, null),
    false,
    null)
    );
    // Save the DACL
    SetProcessSecurityDescriptor(hProcess, dacl);
}

3)Вызываем в любом месте защиту процесса, например при запуске приложения:

public Form1()
{          
    InitializeComponent();
    block();
}

      Для проверки работоспособности данного примера, скомпилируйте ваш проект и запустите полученный файл *.exe, в папке Debug. Запустите диспетчер задач и перейдите во вкладку "Процессы", найдите процесс вашего проекта: 

      Сделайте клик правой клавиши мыши по процессу и выберете из контекстного меню пункт "Завершить процесс". Диспетчер задач, выдаст вам сообщение "Вы действительно хотите завершить ...", выберете "Завершить процесс".

Результат, при попытки завершения процесса будет таким:

Ссылки для скачивания примера: Rusfolder.net - DepositFiles - Turbobit.net - Letitbit.net