Public Shared Function GetPortStatus() As List(Of PortStatus)
        Dim TestPort As SerialPort = New SerialPort, Status As PortStatus
        Dim ports() As String, i As Integer = 0, Objektliste As List(Of _
          PortStatus)
 
        ports = IO.Ports.SerialPort.GetPortNames()          'Ports des Rechners 
        ' ermitteln
 
        Objektliste = New List(Of PortStatus)(ports.Length - 1)
 
        For Each port In ports
 
            Status = New PortStatus
 
            Try
                With TestPort
                    .PortName = port                        'Com 1, 2, ..., n
                    .ReadTimeout = 500                      'ReadTimeout in ms
                    .Open()                                 'Versuchen zu öffnen
                End With
 
            Catch ex As Exception                           'Fehlschlag
 
            Finally
                If TestPort.IsOpen = True Then
                    Status.PortStatus = True
                Else
                    Status.PortStatus = False
                End If
 
                Status.PortName = port
                TestPort.Close()
            End Try
 
            Objektliste.Add(Status)
 
            i += 1
        Next port
        Return Objektliste
    End Function

    Private Sub GibStatusMsg
 
        Dim liste As New List(Of SerPortClass.SerPort.PortStatus), s As String _
          = String.Empty
        liste = SerPortClass.SerPort.GetPortStatus()
 
        For Each obj As SerPortClass.SerPort.PortStatus In liste
            s = s & (obj.PortName & " ist " & If(obj.PortStatus, "verfügbar", _
              "nicht verfügbar")) & vbCrLf
        Next
 
        MessageBox.Show(s)
    End Sub

Ahnungsloser ahnungsloser...