Dyn, the sites' common DNS provider, said its investigation showed that many of the compromised smart devices had been infected with a malware because of inadequate security protections. Since then, manufacturers have been under increased pressure to regularly update firmware on smart devices.

A 2017 report by Parks Associates showed 41 percent of U.S. homes with wifi planned to purchase a smart appliance or other wifi-connected household device in the next 12 months, meaning there are now probably millions more IoT devices than there were at the time of the 2016 attack.

From the article "Poll shows consumers not sure what 'Internet of Things' means" by Mark Huffman.