Computer-to-Computer Networks

Question

I'm on a business trip right now (my first with my new MacBook Pro) and when I clicked on the Airport Extreme icon at top, I noticed much more than just the hotel's wireless connection. There are also a couple "Computer-to-Computer" networks listed. Out of curiosity, I clicked on them individually -- it allowed me to connect to one, superimposing a little computer icon over the Airport Extreme icon at top.
My question is, what did I do when I connected this network? I looked in Finder to see whether something else showed up and there was nothing. I also disconnected the Ethernet cable to see if I could use the Internet through this network and it didn't work. So I'm confused as to what this means. And if it means someone's computer is broadcasting a signal, does it mean that my MacBook Pro is broadcasting a signal too? And would I be able to tell whether someone has connected to my computer?
Sorry if this is all very basic, but I'm still very much a newbie.
Thanks.
MBP 15" 2.0GHz 1GB RAM   Mac OS X (10.4.6)  

Answer 1

Some people who use Internet Connection Sharing at home don't turn it off when they travel, and so that it is then broadcast and you can pick it up.
Most of these computer-to-computer networks are benign, however not all are.
I would recommend to everyone to never connect to them.
I was coming home on the train in November last year when my Sony VAIO said it had found some wireless networks. I usually keep the wireless off to conserve battery.
I checked the wireless networks list.
I was surprised to see these networks as I was on a train and just coming out of Paddington.
Now the first two may have been unprotected home networks that you get when you use a wireless access point out of the box and not configure it.
However the second two look more interesting.
There is no such wireless network as vodafone WLAN hotspot and FREE was a bit suspicious. However the reason they look really suspicious is that these are not wireless access points but computer-to-computer networks which you can tell because of the icons.
This immediately threw up warning bells for me, so I turned my wireless off.
What did concern me was that an innocent passerby could think these were wireless access points (or more scary the computer could join them automatically). There are trains in the UK with wifi access and some train operators use wireless networks for their onboard ticket machines.
These are not true evil twin wireless networks as has often been reported about, but certainly was the first time I had seen something like this.