function ScanFileForString(aFile, SearchString: String; IgnoreCase: Boolean=true;
                           MaxBytesScanned: Int64 = 2097152): Boolean;
const
 MAX_BUFFER_SIZE = 20480; //20 kb
var
 Buffer: String;
 FS: TFileStream;
 BytesRead: Integer;
 i, match: Integer;
 BufferSize, StrLength: Integer;
begin
 Result := false;
 If (SearchString='') then exit;
 If IgnoreCase then SearchString := ANSIUppercase(SearchString);

 //Datei öffnen... falls das nicht klappt gibts hier ne Exception
 //daher die Funktion besser im try..except Schutzblock aufrufen!
 FS := TFileStream.Create(aFile, fmOpenRead or fmShareDenyWrite);

 try
  BufferSize := 0;
  StrLength := Length(SearchString);
  //Ermitteln wie groß der Puffer sein muss. Er soll ca. 20 kb groß sein,
  //wenn nicht die ganze Datei reinpasst
  If FS.Size <= MAX_BUFFER_SIZE then
   BufferSize := FS.Size
    else BufferSize := (MAX_BUFFER_SIZE div StrLength) * StrLength;
  SetLength(Buffer, BufferSize);


  Repeat //Höchstens MaxBytesScanned Bytes untersuchen oder bis EOF

  BytesRead := FS.Read(Buffer[1], BufferSize);
  If BytesRead = 0 then exit;
  If IgnoreCase then Buffer := ANSIUppercase(Buffer);

  for i:=1 to BytesRead do
   begin
    match := 0;
    If (BufferSize-(i-1) >= StrLength) then
    while (Buffer[i+match] = SearchString[match+1]) do
     begin
      inc(match);
      If match = StrLength then
       begin
        Result := true;
        exit;
       end;
     end;
   end;

  Until (FS.Position >= MaxBytesScanned) or (FS.Position = FS.Size);
 finally
  FS.Free;
  SetLength(Buffer, 0);
 end;
end;