[Code]
const
  WINSOCK_2_2 = 514;
  INADDR_NONE = $FFFFFFFF;
  WSASYS_STATUS_LEN = 128;
  WSADESCRIPTION_LEN = 256;

type
  u_long = DWORD;
  #ifndef UNICODE
  AnsiString = string;
  #endif

  TWSAData = record
    wVersion: Word;
    wHighVersion: Word;
    szDescription: array[0..WSADESCRIPTION_LEN] of AnsiChar;
    szSystemStatus: array[0..WSASYS_STATUS_LEN] of AnsiChar;
    iMaxSockets: Word;
    iMaxUdpDg: Word;
    lpVendorInfo: PAnsiChar;
  end;

function WSAStartup(wVersionRequested: Word; var lpWSAData: TWSAData): Integer;
  external 'WSAStartup@ws2_32.dll stdcall';
function WSACleanup: Integer;
  external 'WSACleanup@ws2_32.dll stdcall';
function inet_addr(cp: AnsiString): DWORD;
  external 'inet_addr@ws2_32.dll stdcall';

function IsValidIPv4(const Value: string): Boolean;
var
  Data: TWSAData;
begin
  Result := Value <> '';
  if Result then
  begin
    if WSAStartup(WINSOCK_2_2, Data) = 0 then
    begin
      Result := inet_addr(AnsiString(Value)) <> INADDR_NONE;
      WSACleanup;
    end
    else
      RaiseException('Winsock initialization failed!');
  end;
end;