Web bugs?

Web bugs are small programs that are also parts of the web pages we visit. Web bugs collect information on visitors, such as what topics they are interested in (check below for more interesting insights), what parts they use on the website and how, etc. This data can be later used for multiple purposes like to filter news, display personalized ads, and so on.

Web bugs are sometimes references also as "tracker", "web bug", "web beacon", "clear GIF", "1x1 GIF", "tracking pixel", "pixel tag", "pixel". Perhaps the term tracker is the most prominent name used today.

I like relevant ads. What's the problem there?

Lack of transparency

The most processes related to the collection, use and trade of data are not transparent. In most cases, we do not know what happens with the data, or who use them and how. [1]

Only seemingly free

There have been several studies that showed that ads and web bugs can add a remarkable amount of extra traffic to surfing, but can also make a difference with respect to CPU and battery usage. Thus finally the webizen pays the bill. [2]

Not anonymous

While most companies could claim they gather data anonymously, there have been several studies showing that behavioral information can be used for personal identification or at least tracking user activities. [3]

[1] Web bugs run in the background avoiding being noticed; average webizens have no chance to reveal their presence, unless they use software that could help them. As a result, the whole area lacks transparency. Furthermore if it was otherwise, this was not an area under serious research, and the Data Transparency Lab would not support related projects financially (with up to 50 000 EUR).

[2] There are plenty articles to choose from, like this one here, or this one.

[3] It is a generic false-belief that behavioral attributes are not personally identifying, if they are collected without names and other explicit identifiers. One of the best counterexamples is the Netflix study, where researchers showed that the identity could be re-set for majority of the 500k customers whose anonymous votings have been released. The original publication is available here.

But how would they use what they have on me?

This sounds serious, is there a big business behind it? – Let's see the facts!


Annual revenues in $bn

There is a huge busniess behind web bugs which makes the presence of this technology ubiquitous.

  • The ad revenues reach tens of billions USD per year, which was $49,5bn only in 2014.
  • In year 2014 the mobile ad revenues had a growth of 76%.
  • Even the global financial crisis had a light effect on the ad industry.

Ratio of targeted and regular ads (2011)

Targeted are behind a significant part of all ad revenues and this is heavily expected to grow further.

  • In 2011 only 10% of all ads were targeted.
  • One of keys to success for targeted ads is quite simple: the more the advertiser know about the web user the better targete ads it can provide. Thus web bugs have became more and more sophisticated over the years in order to avoid being turned off, and their numers have also been growing rapidly. According to a study in 2012, there were companies who were estimated to see more than 20% of users' activities .

Ratio of Google-Analytics, Doubleclick,
and Facebook web bugs in the Alexa 500-ban

The web was "swarming" of web bugs even by 2012

  • Researchers found 524 distinct web bugs in Alexa top 500.
  • The total number accumulated up to 7264 web bugs.
  • Web bugs used several trick to increase their efficiency. For example, if they could not mark a browser (as third party cookies were blocked), then they attempted to circumvent settings (by loading their website as a first party for the fraction of a second). Other web bugs cooperated secretly in the background.


IAB Internet Advertising Revenue Report

Lukasz Olejnik, Tran Minh-Dung, Claude Castelluccia. Selling Off Privacy at Auction. 2013. <hal-00915249>

Franziska Roesner, Tadayoshi Kohno, and David Wetherall. 9th USENIX Symposium on Networked Systems Design and Implementation (NSDI), April 2012.

What could I do to be protected?

Web bugs can be deactivated relatively simply. Solutions can be categorized as follows:

  1. blocking utilities: browser extensions can simply block web bugs or make their task much harder. In most cases they provide a high level of privacy, although they could be circumvented.
  2. anonymous browsers: these web browsers were designed to provide complex countermeasures against online surveillance, either when commercial or government parties are considered.
  3. secured systems: live operation systems that were crafted having security and privacy in mind.
Blocking utilities

Ghostery: block web bugs based on a fixed, but frequently updated list. The filtering could be personalized with high granularity, and you might consider turning off the ghostrank option if you take privacy seriously.

NoScript: the professional blocker app, that allows blocking other types of content as well (JavaScript, Flash, etc.).

Anonymous browsers

Firefox: private browsing mode is quite interesting in the newest version of Firefox: it turns of ads and block third party trackers.

JondoFox: anonymous browser designed by german professionals. Portable and has cutting edge technology, coming with a closed system anonymizing service called JondoNym.

Tor Browser: the most well known anonymous browser, which is also portable and fully equipped. Network level anonymization is provided the Onion Routing technology.

Secured systems

Tails: live system that provides high security and privacy way beyond safe web browsing.


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Check out our projects and know more about the secrets of the web!


Visualize the path of your emails, and know who else might read them! Thunderbird extension.

Browser fingerprint
Browser fingerprint

This is a cross browser fingerprint test site, where you can check if you could be tracked even in private mode or not.

PET Portal & Blog

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You can find multiple related resources on the International PET Portal & Blog, and also read more about web tracking and surveillance!

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This feed contains curated tweets on privacy, surveillance and related issues!