Actually, NetBIOS probes may be completely innocent. It depends on how your ISP has setup the network.
If you are on an IP subnet that has someone else running with "File and Printer Sharing" enabled, it is normal to see NetBIOS (ports 13x) probes, unless your ISP has taken the time to block those in the router.
These are easily identified as they will contain the same base IP address of the subnet as yours.
If your ISP is competent, they would be blocking ports 13x from accessing thier clients from the Internet. However, I fond many ISP's don't bother with that type of security precaution.
Complain to your ISP about 13x probes.