This doesn't make sense. How were you able to determine that the files that you trying to transfer using Yahoo mesenger are going to your amiga? Where are they supposed to go? Are you sure that you just forwarded incoming packets to port 80 to the Amiga? What else are your Forwarding( in and out)?
This is a very unlikely story. You really need to clarify your discoveries by actually explaining CLEARLY what you did and how you worked out what happened is actually happening.
For example you could try turning port forwarding for port 80 off and test Yahoo messenger again then turn it on. Then explain here what happened. Also explain how you managed to work out that Yahoo messenger was trying to connect to your Amiga when transfering files.
Remember that when transfering files you need a destination IP for those files to go to. I am guessing that yahoo might have the ability to tunnel through proxy's ( which might exist on port 80 ) when sending files. but at the end of the day the destination IP for the transfer is on the internet and it is unlikely that your Amiga will accept trafic for an IP other than it's own. Especially since it isn't running a Yahoo Client ( or maybe it is, you don't say ).
Your forwarding rules on you machine should always only accept connections bound for that same machine. Let us know what you find.
