I use a private IE window to browse facebook (theoretically no data stored locally). I log in to facebook maybe once every 6 months.
Two months ago, I used Chrome on the same machine to search for Dell computers, a specific model.
Both searches were done on the same network.
I logged in to facebook today, and lo and behold, ads for that specific Dell model (far too specific to be random). How did facebook get this information? Is my internet provider selling all my search history? Is there some other mechanism that I don't know? I thought browser data was isolated.