Private mPing As String = String.Empty
 
    Private Sub TextBox1_TextChanged(sender As System.Object, e As _
      System.EventArgs) Handles TextBox1.TextChanged
        mPing = CType(sender, TextBox).Text
    End Sub
 
    Private Sub CheckBox1_CheckedChanged(sender As System.Object, e As _
      System.EventArgs) Handles CheckBox1.CheckedChanged
        Dim chkd = CType(sender, CheckBox).Checked
        If Not mBGW.IsBusy And chkd Then
            mBGW.RunWorkerAsync()
        ElseIf mBGW.IsBusy And Not chkd Then
            mBGW.CancelAsync()
        End If
    End Sub
 
    Private WithEvents mBGW As New System.ComponentModel.BackgroundWorker With _
      {.WorkerSupportsCancellation = True}
 
    Private Sub BackgroundWorker1_DoWork1(ByVal sender As Object, ByVal e As _
      System.ComponentModel.DoWorkEventArgs) Handles mBGW.DoWork
        Do Until e.Cancel
            Dim result As Boolean = My.Computer.Network.Ping(mPing)
            Debug.WriteLine(String.Format("{0}: {1} - {2}", Date.Now, mPing, _
              result))
            System.Threading.Thread.Sleep(1000 * 3)
        Loop
    End Sub

    Private WithEvents mTimer As New Timers.Timer With {.Interval = 3000}
    Private Delegate Sub AddToTextBoxDelegate(txt As String)
 
    Private Sub CheckBox1_CheckedChanged(sender As System.Object, e As _
      System.EventArgs) Handles CheckBox1.CheckedChanged
        Dim chkd As Boolean = CType(sender, CheckBox).Checked
        mTimer.Enabled = chkd
    End Sub
 
    Private Sub mTimer_Elapsed(sender As Object, e As Timers.ElapsedEventArgs) _
      Handles mTimer.Elapsed
        If My.Computer.Network.Ping(mPing) Then
            Me.AddToTextBox(Date.Now & " Die IP Adresse: " & mPing & " war" & _
              "verfügbar")
        Else
            Me.AddToTextBox(Date.Now & " Die IP Adresse: " & mPing & " war" & _
              "nicht verfügbar")
        End If
    End Sub
 
    Private Sub AddToTextBox(txt As String)
        If Me.InvokeRequired Then
            Me.Invoke(New AddToTextBoxDelegate(AddressOf Me.AddToTextBox), txt)
        Else
            Me.TextBox2.Text &= txt & vbCrLf
        End If
    End Sub