It's important to understand the correlation between "iot" device adoption and the increase in volume of these attacks. The acronym might be new along with tools such as shodan but vulnerable IP devices such as DVRs sitting wide open with default passwords is not. Most devices out there being sold that people associate with "iot" call back to their manufacturer servers (outgoing connection from your home). Botnets are exploiting devices which allow incoming connections not the other way! It could be confusing but it's important to understand this fundamental difference.