It depends on who you ask.

If you ask someone with solid-state physics background, they will probably answer along the lines of Colin McFaul or John Rennie: The fermi level is the same as chemical potential (or maybe one should say "electrochemical potential"), i.e. the energy at which a state has 50% chance of being occupied, while the fermi energy is the fermi level at absolute zero.

If you ask someone with semiconductor engineering background, they will probably give the same definition of "fermi level", but they will say that "fermi energy" means exactly the same thing as fermi level. (The obvious question is, "Then what term would a semiconductor engineer use to describe the fermi level at absolute zero? The answer is, they call it "the fermi level at absolute zero"!)

What's the difference between Fermi Energy and Fermi Level?
We have been asked to evaluate Conversant Tracking.

http://www.conversantmedia.com/solutions/enterprise-solutions

From what I can tell its pretty straight forward tracking, like google re-marketing, you pass them the information you want to via some javascript, and they target your visitors with targeted ads you have set up.

The main issue I have is they require us to point two cnames at their system to allow for "First Party Cookies". 

I know this means all cookies would have to be changed to www.foobar.com, instead of foobar.com, to avoid any issues with information being possible exposed to their end.

But more I was wondering what type of attacks this could open us up to if they had a security issue, if this is more or less secure than google's re-marketings model, and what issues could this cause for us with PCI compliance?

PS We use Braintree and Braintree.js so we are just covered under PCI for handling of Tokens, if that matters at all.
