Как защищать текст в webbrowser от копирования?

Public Class Form1
    Dim WebBrowser1 As mywb
    Dim mymf As MyMessageFilter
    Private Sub Form1_FormClosed(ByVal sender As System.Object, ByVal e As System.Windows.Forms.FormClosedEventArgs) Handles MyBase.FormClosed
        Application.RemoveMessageFilter(mymf)
    End Sub
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        mymf = New MyMessageFilter()
        Application.AddMessageFilter(mymf)
        WebBrowser1 = New mywb
        WebBrowser1.Navigate("www.sina.com")
        Me.Controls.Add(WebBrowser1)
        AddHandler WebBrowser1.Rclick, AddressOf RClickhandler
    End Sub
    Private Sub RClickhandler(ByVal x As Short, ByVal y As Short)
        MessageBox.Show(x.ToString & vbCrLf & y.ToString)
    End Sub
End Class
 
Public Class mywb
    Inherits WebBrowser
    Structure POINTS
        Public x As Integer
        Public y As Integer
    End Structure
    Private Const WM_RBUTTONDOWN As Integer = &H204
    Private Const WM_RBUTTONUP As Integer = &H205
    Private Const WM_LBUTTONUP As Integer = &H202
    Private Const WM_LBUTTONDOWN As Integer = &H201
    Private Const WM_PARENTNOTIFY As Integer = &H210
    Private Const WM_KEYDOWN As Integer = &H100
    Private Const WM_COPY As Integer = &H301
    Public Event Rclick(ByVal x As Short, ByVal y As Short)
    Dim xpos As Short
    Dim ypos As Short
    Protected Overrides Sub WndProc(ByRef m As System.Windows.Forms.Message)
        Console.WriteLine(m.Msg.ToString & "   " & DateTime.Now.Second.ToString)
        If m.Msg = WM_PARENTNOTIFY And GetLoWord(m.WParam.ToInt32) = WM_RBUTTONDOWN Or _
        GetLoWord(m.WParam.ToInt32) = WM_RBUTTONUP Then
            xpos = GetLoWord(m.LParam.ToInt32)
            ypos = GetHiWord(m.LParam.ToInt32)
            RaiseEvent Rclick(xpos, ypos)
            Return
        End If
        MyBase.WndProc(m)
    End Sub
    Private Function GetLoWord(ByVal lngWord As Integer) As Short
        If CBool(lngWord And &H8000) Then
            Return CShort(&H8000 Or (lngWord And &H7FFF))
        Else
            Return CShort(lngWord And &HFFFF)
        End If
    End Function
    Private Function GetHiWord(ByVal lngWord As Integer) As Short
        If CBool(lngWord And &H80000000) Then
            Return CShort((lngWord \ 65535) - 1)
        Else
            Return CShort(lngWord \ 65535)
        End If
    End Function
End Class
 
Public Class MyMessageFilter
    Implements IMessageFilter
    Public Function PreFilterMessage(ByRef m As Message) As Boolean Implements IMessageFilter.PreFilterMessage
        If (m.Msg = &H100 Or m.Msg = &H101) Then
            Return True
        End If
        Return False
    End Function
End Class