I noticed this happening while I was getting a site ready with the AddToAny Drupal module.  Pages would randomly hang in my dev environment and it was trying to contact Media6degrees.  After some Googling I found this was a third party tracking cookie being installed with the AddToAny module.  To disable it in Drupal 7, go to the modules page and click "Configure" next to AddToAny.  Under additional options near the bottom, paste this: