You can read more about them here:
Lucb1e.com :: Cookieless Cookies
Essentially it's another lesser known method for tracking users online that has been around for a couple of years now. Supposedly companies such as Hulu and KissMetrics are using it to continue to track users even if they have deleted cookies from their system. I'm not entirely clear as to how it works but from what I can tell, it piggy backs a unique code onto something like an image.
In other words, typically when you visit a web page your browser is checking to see if you have any parts of that page already in your cache and if so, are there more recent copies on the remote sites servers that is should replace them with or not. It's during this step, that a unique ID pertaining to you is passed along. What's particularly frustrating is that this could theoretically be embedded into just about anything on the page, so there's not really a clear way of identifying what has it or not.
Lucb1e.com :: Cookieless Cookies
Essentially it's another lesser known method for tracking users online that has been around for a couple of years now. Supposedly companies such as Hulu and KissMetrics are using it to continue to track users even if they have deleted cookies from their system. I'm not entirely clear as to how it works but from what I can tell, it piggy backs a unique code onto something like an image.
In other words, typically when you visit a web page your browser is checking to see if you have any parts of that page already in your cache and if so, are there more recent copies on the remote sites servers that is should replace them with or not. It's during this step, that a unique ID pertaining to you is passed along. What's particularly frustrating is that this could theoretically be embedded into just about anything on the page, so there's not really a clear way of identifying what has it or not.