RV50 Open Ports


I have an RV50 and it has some open ports as revealed by a network scanning utility. I can understand why SMTP may be active by why is Netbios and Microsoft DS showing up as ports that the RV50 will respond to? How does the modem use these connections? I am trying to keep our modems as secure as possible and any ideas would be appreciated.

25/tcp closed smtp
137/tcp closed netbios-ns
139/tcp closed netbios-ssn
445/tcp closed microsoft-ds