[Code]
function DownloadFile(const AURL: string; var AResponse: string): Boolean;
var
  WinHttpRequest: Variant;
begin
  Result := True;
  try
    WinHttpRequest := CreateOleObject('WinHttp.WinHttpRequest.5.1');
    WinHttpRequest.Open('GET', AURL, False);
    WinHttpRequest.Send;
    AResponse := WinHttpRequest.ResponseText;
  except
    Result := False;
    AResponse := GetExceptionMessage;
  end;
end;

procedure DecodeVersion( verstr: String; var verint: array of Integer );
var
  i,p: Integer; s: string;
begin
  verint := [0,0,0,0];
  i := 0;
  while ( (Length(verstr) > 0) and (i < 4) ) do
  begin
    p := pos('.', verstr);
    if p > 0 then
    begin
      if p = 1 then s:= '0' else s:= Copy( verstr, 1, p - 1 );
      verint[i] := StrToInt(s);
      i := i + 1;
      verstr := Copy( verstr, p+1, Length(verstr));
    end
    else
    begin
      verint[i] := StrToInt( verstr );
      verstr := '';
    end;
  end;
end;

function CompareVersion( ver1, ver2: String ) : Integer;
var
  verint1, verint2: array of Integer;
  i: integer;
begin

  SetArrayLength( verint1, 4 );
  DecodeVersion( ver1, verint1 );
  SetArrayLength( verint2, 4 );
  DecodeVersion( ver2, verint2 );
  Result := 0; i := 0;
  while ( (Result = 0) and ( i < 4 ) ) do
  begin
    if verint1[i] > verint2[i] then
      Result := 1
    else
      if verint1[i] < verint2[i] then
        Result := -1
      else
        Result := 0;

    i := i + 1;
  end;
end;

function NextButtonClick(PageId: Integer): Boolean;
var
  ErrCode: integer;
  DeXVersion: string;
begin
  // initialize the Result to True to allow the setup to start
  Result := True;
  // if the version file was successfuly downloaded, then...
  if DownloadFile('http://dex.wotanksmods.com/latestver.txt', DeXVersion) then
  begin
    // the version file was downloaded so only now we can compare versions
    if CompareVersion(DeXVersion, '{#MyAppVersion}') > 0 then
    begin
      Result := MsgBox(ExpandConstant('{cm:InfoDeXVersion1} ' + DeXVersion + ExpandConstant('{cm:InfoDeXVersion2}')),
        mbConfirmation, MB_YESNO) = IDNO;
      // hint; do not use 'open' verb; let the Windows Shell decide the default action for HTTP protocol
      if not Result then
        ShellExec('', 'http://goo.gl/uEiRGw', '', '', SW_SHOW, ewNoWait, ErrCode);
    end;
  end;
end;