What is “cetrk.com”?
When I found it at the bottom of my home page, it looked like it might be something to worry about, so I started investigating. It took a while to find the answer, but it turns out that “cetrk” is a domain which used to host Crazy Egg Tracking scripts. Crazy Egg is a site that provides analytics reports. I had tested their tracking service several years ago, then forgotten to remove the script when I stopped using the site.