Core issue
MSN changes the ports dynamically. The access-list command can block the traffic to all the IP addresses and port numbers on which MSN works, in order to block all the connections to that site. The access-list command blocks the connections to the MSN site from the inside to the outside through the PIX Firewall.
Resolution
In order to block access to MSN messenger (instant messaging), try these commands:
access-list block-msn deny tcp any any eq 1863
access-list block-msn deny tcp any host 65.54.239.80 eq www
access-list block-msn deny tcp any host 65.54.239.81 eq www
access-list block-msn deny tcp any host 207.68.178.61 eq www
access-list block-msn deny tcp any host 207.46.3.4 eq www
access-list block-msn deny tcp any host 65.54.183.202 eq www
access-list block-msn deny tcp any host 207.46.96.142 eq www
access-list block-msn permit ip any any
access-group block-msn in interface inside
Note: The IP addresses given are those of the MSN messenger servers IP addresses on port TCP 80.