Cable internet is a broadcast network, every signal from your ISP's exit node is sent to every client attached to that node in your geographically local region (I think this can be a tens or hundreds clients) and vice versa. Your modem only looks for frames that are designated for your modem's MAC address, the rest are ignored but still received.
Same as channels in broadcast tv, everyone is always receiving the signal for all the channels, but they only 'tune in' to their channel. The difference is that your internet modem is only allowed to tune into one channel (designated by its MAC address). I believe each modem has a unique key for modulating/demodulating its signal, and this is used to establish secure communication with the ISP.
In the book "Computer Networking A Top-Down Approach" the following is written: "One important characteristic of cable Internet access is that it is a shared broadcast medium. In particular, every packet sent by the head end travels down- stream on every link to every home and every packet sent by a home travels on the upstream channel to the head end. For this reason, if several users are simultaneously downloading a video file on the downstream channel, the actual rate at which each user receives its video file will be significantly lower than the aggregate cable downstream rate. On the other hand, if there are only a few active users and they are all Web surfing, then each of the users may actually receive Web pages at the full cable downstream rate, because the users will rarely request a Web page at exactly the same time."
tl;dr you already probably broadcast your modulated bank info (if you're on cable).