At TechEd, as you might imagine, there is a lot of wireless noise. There is the conference wi-fi, but there are also a bunch of ad-hoc or computer to computer networks with remarkably similar names. In the wireless list infrastructure and ad-hoc networks have different icons.
You have to question the motives of people trying to fists for wi-fi users like that. while I know better than to go connecting to ad-hoc networks willy nilly, I wanted to remove the risk of accidentally connecting to one with the same name.
In Vista you can, via the command line, filter the list of available wireless networks. To filter out ad-hoc networks run the following from a command line (running as admin, all on one line)
netsh wlan add filter permission=denyall networktype=adhoc
to reverse this again run the following:
netsh wlan del filter permission=denyall networktype=adhoc