Block NetBIOS ports over TCP/IP

Block NetBIOS ports over TCP/IP to all Internet traffic if you need to enable file sharing for your machine so no one from the outside can access the contents of your hard drives through these ports. This can be accomplished with either one of these two methods:

Preferred method: Block incoming and outgoing access to ports 135, 137-139, and 445 with your firewall. ZoneAlarm (a free personall firewall) does this by default when you set the Internet Zone Security to "high". (The "medium" Internet Zone Security default settings only block incoming access to NetBIOS ports and you can manually change that to include outgoing, but remember - any Internet Zone Security setting lower than "high" is not recommended for use in the Internet Zone.)