The best policy and practice is to only run NetMeeting, or any other H.323 teleconferencing system, when it is explicitly needed. Alternatively, a NAT router or personal firewall could be configured to keep ports 1720 and 389 closed until they are needed for NetMeeting conferencing.

Note: NetMeeting's H.323 teleconferencing protocol is extremely NAT router and firewall hostile due to its dynamic assignment of UDP protocol ports for media content streaming. Any network appliance or filtering software must be highly protocol aware to provide effective protection while allowing the protocol to function. You should verify that any NAT router or personal firewall is capable of managing NetMeeting conference connections before investing in any such product's purchase.

For further reading or research:

  http://www.openh323.org/

  http://www.openh323.org/standards.html