Blocking outgoing file sharing protocals
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We can block outgoing connections (TCP & UDP) for the following file sharing applications:

1044   Direct File Express  
1045   Direct File Express  
1214   Kazaa, Grokster  
4329   iMesh  
4661   Edonkey 2000  
4662   "  
4665   "  
6346   BearShare, Gnucleus, Morpheus, Swapper, XoloX, LimeWire,  
   Phex, Gnewtellium, Gtk-Gnutella, Mutella, Qtella  
6347   "
6666   Yoink
6667   Yoink
6699   AutoNap, BeNapster, Napster, Crapster, Duskter, Gnap,
   Gtk Napster, Hackster, iNapster, Jnap, WinMX
6700   "
6701   "
7668   Aimster / Madster
7788   BuddyShare
8311   Scour
8888   AudioGnome, OpenNap, Swaptor
8889   AudioGnome, OpenNap
28864   hotComm
28865   hotComm
41170   Blubster

We will block access to these services by adding the following lines to the beginning of the pf.conf file:

ports_ptp = "{ 1044, 1045, 1214, 4329, 4661, 4662, 4665, 6346, 6347, 6666, 6667, 6699, 6700, 6701, 7668, 7788, 8311, 8888, 8889, 28864, 28865, 41170 }"

block out on $ext_if proto { tcp, udp } from $internal_net to any port $ports_ptp

It is important to note that some file sharing applications/protocols, most notable Kazaa, will dynamically switch and use different ports (including HTTP 80) when they are unable to talk to the servers. The rules above may therefore only prevent certain less sophisticated protocols. For more information on how to prevent Kazaa please search the Misc OpenBSD mailing list, Google Groups or wait for an updated version of this document.