I don’t want to freak you out about tracking cookies, but you know that ads appear on your sites based on the sites you’ve been to right?
Hyper-targeting baby.
Also, this would be a good time to pitch the Adblock Plus plugin which blocks ads from most sites. I didn’t even know Core had ads. 
If you want to really become sketched out, your mobile traffic, location data, and even voice info can and will be used to feed you ads.