A seguir, há apenas a citação de duas fontes diferentes que usei para desabilitar a porta 445 com êxito nas máquinas com Windows XP. Eu estava fechando a porta 445 e 135, 137 - 139, então segui todas as instruções do artigo e funcionou para mim.
Informações gerais sobre a porta 445 (link do arquivo)
Among the new ports used by Windows 2000 is TCP port 445 which is used for SMB over TCP. The SMB (Server Message Block) protocol is used among other things for file sharing in Windows NT/2000/XP. In Windows NT it ran on top of NetBT (NetBIOS over TCP/IP), which used the famous ports 137, 138 (UDP) and 139 (TCP). In Windows 2000/XP, Microsoft added the possibility to run SMB directly over TCP/IP, without the extra layer of NetBT. For this they use TCP port 445.
At its simplest NetBIOS on your LAN may just be a necessary evil for legacy software. NetBIOS on your WAN or over the Internet, however, is an enormous (read foolish...) security risk. All sorts of information, such as your domain, workgroup and system names, as well as account information is obtainable via NetBIOS. It really is in your best interests to ensure that NetBIOS never leaves your network.
If you are using a multi-homed machine i.e. more than 1 network card, then you should disable NetBIOS on every network card, or Dial-Up Connection under the TCP/IP properties, that is not part of your local network.
Como desabilitar a porta 445
To disable Port 445:
Add the following registry key:
Key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\NetBT\Parameters Name: SMBDeviceEnabled Type: DWORD (REG_DWORD) Data: 0
Don’t forget to restart your computer after disabling the above ports for effect. Also, to check that those ports are disabled, you can open a command prompt and type netstat -an to confirm that your computer is no longer listening to those ports.
(as chaves de registro são diferentes para o Windows 7 em diante, consulte este documento Artigo da Microsoft )