Visual Basic.NET - Desactivar boton cerrar del formulario

Hola,
Como puedo desactivar en tiempo de ejecución el boton "X" cerrar del formulario.
Gracias.

Hola....

Puedes usar este código

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Private Declare Function GetSystemMenu Lib "user32.dll" ( _
ByVal hWnd As IntPtr, _
ByVal bRevert As Int32 _
) As IntPtr

Private Declare Function GetMenuItemCount Lib "user32.dll" ( _
ByVal hMenu As IntPtr _
) As Int32

Private Declare Function DrawMenuBar Lib "user32.dll" ( _
ByVal hWnd As IntPtr _
) As Int32

Private Declare Function RemoveMenu Lib "user32.dll" ( _
ByVal hMenu As IntPtr, _
ByVal nPosition As Int32, _
ByVal wFlags As Int32 _
) As Int32

Private Const MF_BYPOSITION As Int32 = &H400
Private Const MF_REMOVE As Int32 = &H1000

Private Sub RemoveCloseButton(ByVal frmForm As Form)
Dim hMenu As IntPtr, n As Int32
hMenu = GetSystemMenu(frmForm.Handle, 0)
If Not hMenu.Equals(IntPtr.Zero) Then
n = GetMenuItemCount(hMenu)
If n > 0 Then
RemoveMenu(hMenu, n - 1, MF_BYPOSITION Or MF_REMOVE)
RemoveMenu(hMenu, n - 2, MF_BYPOSITION Or MF_REMOVE)
DrawMenuBar(frmForm.Handle)
End If
End If
End Sub
///

Saludos