VB - Dateien sicher löschen

Imports System.IO
Imports System.Text
Imports System.Threading
    Public Class SafedeleteFunction
        Public Property DelThread As Thread
        Public Function SafeEraser(filepath As String, repeat As Integer, delete As Boolean)
            Dim r As New Random
            Dim sb As New StringBuilder
            Dim abc = "abcdefghijklmnopqrstuvwxyz"
            Try
                For i = 0 To repeat
                    Dim idx As Integer = r.Next(0, abc.Length)
                    Dim filesize As New FileStream(filepath, FileMode.Open)
                    Dim fsize = CInt(Int(filesize.Length))
                    filesize.Close()
                    Dim fstream As New StreamWriter(filepath)
                    sb.Append(abc.Substring(idx, 1))
                    For o = 0 To CInt(fsize)
                        fstream.Write(sb.ToString)
                    Next
                    sb.Clear()
                    fstream.Close()
                Next
            Catch ex As Exception
            End Try
            Try
                If delete = True Then
                    File.Delete(filepath)
                Else
                End If
            Catch ex As Exception
                MsgBox("File could not be deleted: " & ErrorToString(), MsgBoxStyle.Critical)
            End Try
        End Function
    End Class