There is a thread at Webmasterworld where some members doing som reverse engineering on Google AdSense source codes. A member noticed many variables that were being passed to Google from the AdSense iframe. A sample of them are:
client = Publisher Id, Identifies which account to credit the ad click
dt =? Its a number that changes. Maybe the time?
lmt =? Also a number that changes.
format = Type of ad format used. Links, Ads, maybe other types too. Includes dimensions.
output = "html". I presume its different for RSS ads? Is this always html for html embedded ads?
channel = Unique id to represent which Ad channel to credit the click.
url = The page the ad was displayed on.
color_bg = The background color (hexadecimal) of the ad.
The member stated he was curious about the finding so that "Since this is a piece of information I can know about when a user clicks an ad, I want to be able to get this information so I analyze it to help me optimize my ads."
There has been some development in finding the meaning of these codes. However, another member pointed out that reverse engineering of AdSense ads is prohibited under Section 15.