You have likely noticed that the banner ads and other forms of advertisements on many of the web pages visited appear to "coincidently" be for many of the same items that you have recently searched for online. You may even notice that many of these ads are also from many of the same online sellers whose web pages you have recently visited. In some cases, you may also see online ads for direct competitors of previously visited websites, offering many of the same or similar products that you have looked at on other websites. It should not be surprising that the owners of many websites, as well as many third party advertisers, use a variety of tracking technologies to gather information on you, as an individual, the types of websites that you visit, and the products and services viewed. While many users find this targeted advertising interesting and useful, and even possibly necessary in order to support "free" web sites and online services, many others consider the gathering of such personal information as a gross violation of personal privacy.
Some of the more common methods of compiling and distributing this personal information and shopping preferences are the placement of "tracking cookies" on the user's device; web bugs or web beacons (small graphic files which transmit information when opened, often 1 pixel in size); and the dissemination (sale) of personal information entered on a website. Cookies are small, alpha-numeric and text based pieces of data which are by default, placed on the hard drive or other storage of the device being used to view a website; while some types of cookies are benign and necessary to compile shopping carts, store passwords and other login information, and save other information that can speed the web process, some other types of cookies may not be so desirable.
The most common type of unwanted cookies is often known as "tracking cookies", which are typically placed on the hard drive or other storage medium, just as other cookies, but these cookies can also be read by other third parties as a method of gathering information about the user, mostly for targeted marketing purposes. There are many companies that have a lucrative and highly profitable business selling access to the tracking cookies which they have previously been placed in storage, most often by simply visiting a web page. Almost all browsers give the users the option to control which cookies can be saved and accessed, but the default is to accept all cookies. Tracking cookies that are currently saved in the device storage can often be easily and quickly removed by most of the reputable (and often free) security scanners, such as Malwarebytes and SuperAntiSpyware.
What many users might find shocking is that they unknowingly and explicitly allowed many of the websites that they visit to place tracking cookies and other marketing information on their computers and smart devices. When I mention this to users at some of my security and privacy presentations, some of those present get very agitated, and vehemently deny that they ever gave permission for websites to place such information on their computers and other devices. My typical response is something to the effect of "Did you ever read the privacy statement on those websites when displayed, or simply click on the "I Agree" box when first visiting them?" Most of the honest, but still aggrieved users, acknowledge that they never fully read the privacy statements on the websites visited, with the typical response being that the privacy statement is too long to read, or it is written in "legalese" which they cannot readily understand, so they simply "agree" in order to get access to that particular website.
PrivacyCheck is an excellent method to determine what commercial websites are really doing with your personally identifiable information (PII), but its major weakness is that it (currently) only works with the Chrome web browser. Users of other browsers may find some privacy utilities that provide significant privacy protection while online.
On all of my PCs, as a browser add-on, I have been using a free, popular browser extension called "Ghostery", which will seamlessly run on computers using any of the major and popular browsers including Firefox, Chrome, Opera, Safari, and Internet Explorer, as well as on mobile devices running the Android and iOS operating systems. According to its website, Ghostery claims to have, "The largest tracker database on the internet, constantly growing; Ghostery has the largest tracker database available on the web. We meticulously select, profile and cull over 2,000 trackers and 2,300 tracking patterns." Ghostery displays the tracking information on almost every web page opened, and gives the user the ability to allow or block trackers as desired.
Our personal privacy should be taken very seriously. Once third parties have access to our personal information, it is virtually impossible to get it back. Most of the browsers offer an option or setting to control privacy, which may be called "Do Not Track", "Reject Third Party Cookies", or some similar name. By using PrivacyTracker, Ghostery, browser privacy settings, and other utilities, our individual privacy may be better protected.