After digging around for open ports I have found TCP port 445 open on one of my machines. For what this port is used? The answer was here:
What’s TCP port 445 used for in Windows 2000/XP?
“Among the new ports used by Windows 2000, Windows XP and Windows Server 2003, 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/2003, Microsoft added the possibility to run SMB directly over TCP/IP, without the extra layer of NetBT. For this they use TCP port 445.
Then found this article:
How can I configure TCP/IP networking while NetBIOS is disabled in Windows 2000/XP/2003?
Perfect! Petri IT Knowledgebase
If you are interested in the topic references are very good source of information.