How can i block connection of Yahoo Messenger from a router?

    I need to block (prevent) from a router the acces (connection) of Yahoo Messenger program installed on a computer from the local network.
     Is it possible?

   Thank you!
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theoaksConnect With a Mentor Commented:
yahoo messenger uses port 5050, then 80 then random, which means you need something smarter like isa to inspect the http packet for its content type. blocking ports wont work unless you want to block the rest of the internet.

some dogey ways like putting flase host entries or dns records for the messenger domains could work.

Hello Cristi_E,

Here are some details on the ports Yahoo Messenger uses:-


kyodaiConnect With a Mentor Commented:
Yahoo messenger unfortunately tries a wide range of possible ports and can even connect through Port 80. Your best bet would be to block traffic to ports 5000-5050 and access to and, that should do the trick.
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The suggestion being of course to block these ports on your router. I'd start with port 5050 and 5101
robmonster: that simply wont work.

if you block every single port other than 80, it will still get out! if you then block 80 as well, nothing will work! not even allowed web traffic!

you need to filter the packet at a different level re: my previous suggestions
RobmonsterConnect With a Mentor Commented:
Yes, it would seem that Yahoo messenger has 'evelved' and tries to get around port blocks...

Here is a site describing the use of OpenDNS to block a list of IM related domains at DNS level. If you are not using OpenDNS then the list of addresses might still be useful
Cristi_EAuthor Commented:
Thank you verry much!
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