Adesnes cookie?

Do they drop one?

[benflux]

Do Google plant a cookie on your visitors PC to see if they come back and click later on?

Ben.

[jomaxx]

If you're talking about the equivalent of "return days" for an affiliate program, the answer would be no. AdSense displays the ad and the user must click then and there.

If you're talking about Google tracking how many ads the same user clicks on, I'm sure they pay attention to that in general but I don't think the specifics of how they do it are that important.

[transactiongeek]

I am sure that google tracks how many ads an IP address clicks on.

It would be the fundamental underpinning of detecting sophisticated fraud.

[Jenstar]

They do use cookies for their conversion tracking, for the advertisers who have selected that option in their Adwords account.

From Adwords:
How does Google use cookies in conversion tracking?
The cookie that Google adds to a user's computer when he/she clicks on an ad expires in 30 days. This measure, and the fact that Google uses separate servers for conversion tracking and search results, protects the user's privacy.

Users who don't wish to participate in tracking activities can easily not accept this cookie by setting their Internet browser user preferences. These users will simply not be included in your conversion tracking statistics.

There is a FAQ on the whole conversion option, privacy info in relation to this, and a whole lot more details at
[adwords.google.com...]

[louai]

I am sure that tracking cannot be as simple as IP tracking but rather a combination of factors.

1. Store IP: At the very least the first two tuples of the IP 255.255.0.0
(i.e. AOL uses a proxy which mostly changes the last tuple of the IP address, however it sometimes affects the bottom 2 tuples)
2. Resolve to common ISP block (part of the IP check)
3. Store: the User Agent Log (Browser, plugins, OS)
(Sometimes the same IP is reused with other users, so using the User Agent field can help identify different users)
4. Using a cookie.

None of the methods above are foolproof but they do provide a general overall picture of the user activity.
I would not know to what extent if they use those methods above or other methods though I suspect that they do.

I am sure they are probably developing/applying a heuristic method to flag activity that requires closer attention. Something similar to what anti-virus programs do.

[richmondsteve]

louai, I agree that Google's fraud detection isn't simply based on counting clicks from IP addresses and I'm quite sure transactiongeek wasn't suggesting it was. Given Google's skilled employees and data from the Google Toolbar I'm sure they're capable of detecting patterns and identifying outliers that most of us couldn't even fathom.