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Ports to block to prevent IM on network

What ports do I need to block to attempt to prevent IM on my network?

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To prevent IM, try the following:

AOL: In and outbound TCP port 4443
AOL: *ALL access to on all port

.NET: In and outbound TCP 6891
.NET: UDP Ports 13324 & 13325
.NET: TCP Port 1503

Yahoo: Block all in and outbound TCP Port 5010
Yahoo: *ALL *.msg.*

AOL.ICQ: Block In and out TCP Ports 5190 & 4001, UDP 4000
AOL.ICQ: Block ports 3474 and 7320 for TCP
AOL.ICQ: Block all TCP 5190, 4001 & UDP 4001 & 4000 to

Further information can be found at

For more information on this topic, visit these other resources:
Best Web Links: Secure messaging
News & Analysis: The risk and intrigue of IM to the enterprise
Web Security Tip: Prevent hackers from sneaking in through IM

This was first published in August 2002

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