Poxbox.net has an ad for coinhive.com on their site. That ad has javascript malware that runs a miner script. Basically this script borrows some of your computing power to mine bitcoins (or some other crypto). Slows the site to a crawl and even when you leave will continue to leech computing power and slow your browser.
Note that you have to opt-in to Adblock's blocking of cryptocurrency miners. At least, I had to opt in specifically - maybe it's default for new installs.
I didn't have to do anything like that on my end - I guess that my initial settings just disabled everything invasive.
