How online tracking cookies build family profiles

In a blog post published today, Mozilla product manager Karen Kim describes an experiment she conducted to see how many tracking cookies were installed on her browser when she was researching a family trip for two adults and two children to Costa Rica.

By visiting multiple flight, hotel and car rental comparison sites and using Google to find sightseeing information, travel tips for traveling with children, and product recommendations, Kim collected a total of 1,620 cookies — about 20 percent of which were tracking third-party cookies from analytics and advertising companies such as Google and Facebook. Kim concluded that there was something “insidious” about the whole situation, saying: “In the process of planning a trip online without tracking protection, someone out there already knows the ages of your children, your partner’s interests, which family is taking a diving lesson, which you booked and with whom.’

While some cookies are critical to keeping modern websites functioning, others are a little more sinister. Good cookies track things like your preferred language and the contents of your shopping cart and keep you logged in when you browse a site. No one really has a problem with these types of cookies – they are a necessary part of the modern web. Without them, all but the most basic websites would cease to function.

Third-party tracking cookies, on the other hand, are the type of cookie that privacy experts are most concerned about. Combined with other types of tracking, they allow companies and data brokers to create incredibly detailed profiles of your online activities. In the Mozilla blog post, Kim said advertising companies could link the ages of her children, her partner’s interests and the tours she booked together. In theory, the information would be anonymous because it would likely be associated with a username rather than their name and address, but these anonymous profiles are surprisingly easy to de-anonymize.

Worse, though, the same companies may have created profiles for her hypothetical children as well. This process starts early. Period and fertility tracking apps – currently under a lot of scrutiny due to the overturning of Roe V Wade in the US – essentially start collecting information about children before they’re even born. As their parents search the web for answers to parenting questions, vacation bookings and all, that profile grows. Some companies even collect and sell data from children while they take classes online. One pre-pandemic report found that by the time a child turns 13, more than 72 million pieces of personal data will be collected about them. That figure is almost certainly higher now.

To counter this, Kim suggests using Firefox, which has full cookie protection — a special browser mode that sets cookies aside to prevent third-party tracking cookies from following you around the web — enabled by default. However, most modern browsers offer similar features. Safari blocks all cross-site tracking, including cookies, by default with a feature called Smart Tracking Prevention. Brave, Opera and the new DuckDuckGo browser use similar strategies to block third-party cookies while allowing websites to function normally. Even Microsoft Edge has an option, but you’ll need to enable its stricter settings. The only real holdout is Google Chrome (unsurprisingly) – but even that should start blocking them next year.

Cookies as a tracking tool are on the way out. Very soon, only users with old and outdated versions of web browsers will be able to be tracked through them. The bigger problem, unfortunately, is that tracking continues to evolve. Soon there may be a whole host of alternative tracking tools that will need to be avoided. In particular, first-party tracking by the websites you visit is very difficult to prevent. And while you can block cookies, it’s impossible to prevent Google from knowing everything you do in Google products like Gmail and YouTube. If you’re signed in to your account, they can see every YouTube video you watch, every document you share, and what you search for.

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