Well, no one else has answered, so I'll give it a shot: netbios-ssn is the port that SMB uses for filesharing. SMB is the name of the protocol that Windows uses for filesharing and other messaging tasks. The SMB protocol is implemented on Linux by the Samba package. If you don't have a specific reason to run Samba on your Linode (in other words, if you aren't using your Linode for windows filesharing), then you should probably disable it. On RedHat this can be done by running:

/etc/init.d/smb stop

chkconfig smb off

On Debian I would stop the service and just remove the package.

-"Zow"

Thanks very much zow.

I'll have a go at that now :)