These are nasty things. Some info is available here:
https://anonym.to/?https://github.com/samyk/evercookie
I am not sure if they are still effective and in use today:
- Nobody uses Java in the browser anymore
- Very few use Flash
- Most ad blockers should block the scripts
- There are other techniques out there to identify users without any cookies, e.g browser fingerprinting.
How do you know that you have one?
This might give a hint where it is stored and how to remove.