CheckBox1.CheckState = CheckState.Checked

Dim WithEvents BackgroundWorker1 As New System.ComponentModel.BackgroundWorker _
  With {.WorkerReportsProgress = True, .WorkerSupportsCancellation = True}
 
Private Sub BackgroundWorker1_DoWork1(ByVal sender As Object, ByVal e As _
  System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork
 
        Dim IPPingMonitoringResult As Boolean
 
        While CheckBox1.CheckState = CheckState.Checked
            IPPingMonitoringResult = My.Computer.Network.Ping(TextBox1.Text)
 
            If IPPingMonitoringResult = True Then
                LogFileEintrag = (Now & " Die IP Adresse: " & TextBox1.Text & "" & _
                  "war verfügbar")
                LogFileEintragSchreiben()
 
            ElseIf IPPingMonitoringResult = False Then
                LogFileEintrag = (Now & " Die IP Adresse: " & TextBox1.Text & "" & _
                  "war nicht verfügbar")
                LogFileEintragSchreiben()
 
            End If
 
            System.Threading.Thread.Sleep(1000 * 60) 'Wartedauer bis zur 
            ' nächsten Wiederholung in ms * 1000
        End While
    End Sub

CheckBox1.CheckState = CheckState.Unchecked

If CheckBox1.CheckState = CheckState.Unchecked Then        
            BackgroundWorker1.CancelAsync()
End If