Websites can use whether or not a resource is cached (one way to measure that is how long it takes to load) to uniquely identify your browser and track you across the internet.
Another attack is to determine if you visited $popularWebsite by checking if resources it uses are cached (this could be useful to, for example, the Chinese government for surveillance on its citizens).
Another attack is to determine if you visited $popularWebsite by checking if resources it uses are cached (this could be useful to, for example, the Chinese government for surveillance on its citizens).