Pretend you are the lead detective on a hit new show, “CSI: Terrible Stuff on the Internet.” In the first episode, you set up one of those crazy walls plastered with headlines and headshots, looking for hidden connections between everything awful that’s been happening online recently.

There’s a lot of dark stuff. In one corner, you have the Russian campaign to influence the 2016 presidential election with digital propaganda. In another, a rash of repugnant videos on YouTube, with children being mock-abused, cartoon characters bizarrely committing suicide on the kids’ channel and a popular vlogger recording a body hanging from a tree.

Then there’s tech “addiction,” the rising worry that adults and kids are getting hooked on smartphones and social networks despite our best efforts to resist the constant desire for a fix. And all over the internet, general fakery abounds — there are millions of fake followers on Twitter and Facebook, fake rehab centers being touted on Google and even fake review sites to sell you a mattress.

So who is the central villain in this story, the driving force behind much of the chaos and disrepute online?