procedure TForm1.Button1Click(Sender: TObject);
var s:string;
    i,j,len:integer;
    x:char;
begin
  randomize;
  len := length(memo1.text);
  setlength(s,len);
  s := memo1.text;

  for i := 1 to len-1 do
      for j := i+1 to len do
          if random(31337) mod 7 = 0 then begin
             x := s[i];
             s[i] := s[j];
             s[j] := x;
          end;
    Memo1.Text := s;
end;