Function RndString( _
    Optional Chars As String = "0123456789", _
    Optional MinLen As Long = 1, _
    Optional MaxLen As Long = 2) As String
  Dim CharsLen As Long
  Dim i As Long
  Dim n As Long
 
  'Länge(n) bestimmen:
  CharsLen = Len(Chars)
  n = Int((MaxLen - MinLen + 1) * Rnd) + MinLen
  RndString = Space$(n)
 
  'Zufällige Zeichen einfügen:
  For i = 1 To n
    n = Int(CharsLen * Rnd) + 1
    Mid$(RndString, i) = Mid$(Chars, n, 1)
  Next i
End Function
 
Private Sub Command1_Click()
Text1.Text = RndString
Dim intFile As Integer
Dim bytArr() As Byte
 
'// den Bytearray eben entsprechend
'// dimensionieren und befüllen
ReDim bytArr(786432)
Dim o As Long
For o = 0 To 786432
bytArr(o) = RndString
Next o
'// Bytearray in Datei schreiben
intFile = FreeFile
Open "C:\Testmuster.usm" For Binary As #intFile
Put #intFile, , bytArr
Close #intFile
 
End Sub