Nothing more than available networks that you can choose to connect to, if you have the correct credentials. Note that other people's phones can also act as such networks (if they have been silly enough to configure this as an openly broadcast network) so that's why you sometimes see more options turning up when people walk past.
Strange things in junk mail? Nothing to do with your wifi networks, more likely linked to your surfing habits and sites where you left your e-mail address
