NOTE: This page is an archive of work completed in 2015
Our goal is to define and quantify vectors for tracking consumers on the internet. By doing this, using consistent methods over time, we will be able to make empirical statements about the state of internet tracking and privacy.
Web Privacy Census Links
Public policymakers are proposing measures to give consumers more privacy rights online. These measures are based upon the assumption that the web privacy landscape has become worse for consumers; that their online activities are tracked more pervasively now
than they were in the past. This assumption may be true, as online advertising and metrics companies have developed more sophisticated ways to track and identify individuals online. This has been substantiated in the academic literature, and in the popular press through an influential news series, “What they Know,” by Wall Street Journal reporters.
As policymakers consider different approaches for addressing internet privacy, it is critical to understand how interventions such as negative press attention, self-regulation, Federal Trade Commission enforcement actions, and direct regulation affect tracking. As early as 1995, Beth Givens of the Privacy Rights Clearinghouse suggested that federal agencies create benchmarks for online privacy. The first attempts of web measurement, discussed in our literature review, found relatively little tracking online in 1997–only 23 of the most popular websites were using cookies on their homepages. But within a few years, tracking for network advertising was present on many websites, and by 2011, all of the most popular websites employed cookies.
The Web Privacy Census is intended to formalize the benchmarking process and measure internet tracking consistently over time. We seek to explore:
- How many entities are tracking users online?
- What vectors (technologies) are most popular for tracking users?
- Is there displacement (i.e. a shift from one tracking technology to another) in tracking practices?
- Is there greater concentration of tracking companies online?
- What entities have the greatest potential for online tracking and why?
This effort was developed and executed in partnership with Abine, Inc. Abine has been our technical collaborator and resource partner, helping us develop a reliable method for web crawling and analysis of tracking vectors. This project is supported by and builds upon prior research in collaboration with the National Science Foundation Team for Research in Ubiquitous Secure Technology.
Results and Discussion
This report contains data from our crawl conducted on 10/24/12, and compares it to the results of our June 2012 Web Privacy Census.
We conduct two different crawls—a shallow one where our test browser just visits the homepage of a site, and a deep crawl where our browser visits six links on a site.
We found cookies on all popular websites (by “popular websites,” we mean the top 100 most popular according to Quantcast). Historically, there has been a large upswing in cookies on popular websites. When we first measured cookies in 2009, we found 3,602 cookies on popular websites, and in 2011, we found 5,675.
Here we found statistically significant upticks in tracking mechanisms from just five months ago: more popular sites are using more cookies. We found a total of 6,485 cookies on the top 100 websites; the vast majority of these cookies are from third party domains.
|Deep Crawl – Most Popular 100 Sites (six links deep)|
|Total HTTP Cookies||5,795||6,485||up ↑|
|Total HTTP Cookies: First Party||932||992|
|Total HTTP Cookies: Third Party||4,863||5,493||up ↑|
|Total Flash Cookies||23||17|
|Total Flash LSO: First Party||8||6|
|Total Flash LSO: Third Party||15||11|
|Total Session Cookies||301||259|
|Total HTML5 LSO||34||38|
*We only indicate trends that are statistically significant at the .05 level or stronger.
|Key Tracking Metrics – Most Popular 100 Sites|
|Do all popular sites have cookies?||Yes||Yes|
|Sites with 100 or more cookies||21||21|
|Sites with 150 or more cookies||6||11|
|Percentage of cookies set by a third party host||84%||84.7%|
|Number of third party hosts||446||457|
|Number of top websites with a Google presence||78||74|
|Number of sites with Flash cookies||13||11|
|Number of sites with HTML5 storage||34||38|
|Number of sites without third party cookies||4||5|
We are observing an overall downward trend in the use of Flash cookies. In 2011, 37 sites used Flash cookies. In our May 2012 crawl, 13 were, and now just 11 use Flash cookies. Websites may be changing strategies here by adopting HTML5 local storage. In 2011, when we first surveyed local storage, we found only 17 sites using HTML5. Our May 2012 crawl found 34, and now 38 sites are using HTML5 local storage.
|Top Trackers – Most Popular 100 Sites|
Google’s DoubleClick leads the top trackers statistic in all three crawls.
|Trackers Setting the Most Cookies – Most Popular 100 Sites|
|Bluekai(321 cookies)||bluekai.com (328 cookies)|
The most frequently appearing cookie keys were: ,” “, “, ““, and .” Many of these keys are commonly associated with unique user tracking and Google Analytics. For instance, __utma is used by Google for identifying unique visitors.
|Shallow Crawl – Most Popular 100 Sites|
|Total HTTP Cookies||2616||3152||up ↑|
|Total HTTP Cookies: First Party||729||828||up ↑|
|Total HTTP Cookies: Third Party||1887||2324||up ↑|
|Total Flash Cookies||6||7|
|Total Flash LSO: First Party||3||2|
|Total Flash LSO: Third Party||3||5|
|Total Session Cookies||236||257|
|Total HTML5 LSO||27||34|
Top 1,000 Websites
We observed increased presence of trackers in our crawl of the top 1,000 websites as well. The total number of first and third party cookies placed on computers was up significantly.
|Deep Crawl – Most Popular 1,000 Websites|
|Total HTTP Cookies||62,755||65,381||up ↑|
|Total HTTP Cookies: First Party||8,302||8,658||up ↑|
|Total HTTP Cookies: Third Party||54,453||56,723||up ↑|
|Average HTTP Cookies: First Party||8.32||8.69|
|Average HTTP Cookies: Third Party||54.61||56.95|
|Total Flash Cookies||176||181|
|Total Flash LSO: First Party||44||41|
|Total Flash LSO: Third Party||132||140|
|Total Session Cookies||2,767||2,448||down ↓|
|Total HTML5 LSO||311||318|
Key tracking metrics remains level among the top 1,000 websites.
|Key Tracking Metrics – Most Popular 1,000 Websites|
|Percentage of sites with cookies||97.4%||97.9%|
|Sites with 100 or more cookies||191||198|
|Sites with 150 or more cookies||117||114|
|Sites with 150 or more cookies||87%||86%|
|Number of sites with a Google presence||712||733|
|Number of sites with Flash cookies||110||97|
|Number of sites with HTML5||311||318|
|Number of sites without third party cookies||69||69|
The trackers present in the top 1,000 sites are consistent with those predominating the top 100.
|Most Prevalent Trackers – Most Popular 1,000 Sites|
|Doubleclick.net(685 sites)||Doubleclick.net(681 sites)|
|Trackers Setting the Most Cookies – Most Popular 1,000 Sites|
|Bluekai(2,906 cookies)||Bluekai(2,562 cookies)|
The most frequently appearing cookie keys were: , ,” c,” z,” and
Top 25,000 Websites
Our crawl of the top 25,000 websites is shallow—we only visit the
homepage of these websites. The goal was
to get a basic understanding of cookie counts for a wider range of sites to
develop an understanding of trackers in the long tail.
|Shallow Crawl – Most Popular 25,000 Sites|
|Total HTTP Cookies||442047||476492||up ↑|
| Total HTTP Cookies: First
| Total HTTP Cookies: Third
|Total Flash Cookies||441||454|
| Total Flash LSO: First
| Total Flash LSO: Third
|Total Session Cookies||33,404||33,918||up ↑|
|Total HTML5 LSO||2,417||2,758||up ↑|
We saw an increase in the number of sites that placed 150 or more cookies.
|Key Tracking Metrics – Most Popular 25,000 Websites|
|Percentage of sites with cookies||87%||87%||up ↑|
|Sites with100 or more cookies||730||771|
|Sites with 150 or more cookies||133||267||up ↑|
|Percentage of cookies set by a third party host||76%||76%|
|Number of sites with a Google presence||8,993||9252|
|Number of sites with Flash cookies||344||351|
|Number of sites with HTML5||2417||2758||up ↑|
|Most Prevalent Trackers – Most Popular 25,000 Sites|
|Doubleclick.net(8,554 sites)||Doubleclick.net(8,855 sites)|
|Trackers Setting the Most Cookies – Most Popular 25,000 Sites|
|Bluekai(18,142 cookies)||Doubleclick.net(17,690 cookies)|
The most frequently appearing cookie keys were: “__utmb,” “__utma,” “__utmc,” “__utmz,” “UID.”
In this first update to our original June 2012 Web Privacy Census, we observed statistically signifiant increases in the amount of tracking on all three of our samples–the top 100, 1,000, and top 25,000 websites. Flash cookies use is declining among the most popular websites, and HTML5 local storage is rising across all three groups.
This work was supported in part by TRUST, Team for Research in Ubiquitous Secure Technology, which receives support from the National Science Foundation (NSF award number CCF-0424422).
How to cite this report:
Chris Jay Hoofnagle & Nathan Good, The Web Privacy Census , October 2012, available at