Another Way to Track Users Online: UID Smuggling

words Al Woods

For decades, advertisers and web trackers have used cookies in our browsers, helping them compile data on the websites we visit. Hence, careful tracking also allowed them to build our digital profiles. However, more privacy-focused browsers already block third-party cookies by default.

On the one hand, such blocking poses a significant challenge to businesses. It becomes difficult for them to place ads online as they cannot correctly say which users would be interested in their products.

Also, with Google Chrome also choosing to eliminate third-party cookies, companies look for alternatives. And in some cases, these options refer to alternative tracking methods.

UID Smuggling tracking

The Introduction to UID Smuggling

Advertisers did manage possible ways to replace cookies. The new method known as UID smuggling lets entities track users online without relying on third-party cookies. However, most users are still in the dark regarding how frequently UID smuggling is being used to track our online behavior.

A new measurement tool referred to as CrumbCruncher was developed by researchers at UC San Diego to quantify how often UID smuggling was occurring in the wild. CrumbCruncher poses as a regular internet user, and while navigating, it keeps an eye on the number of times UID smuggling has been used for tracking it.

It was revealed that of all the navigations CrumbCruncher made, UID smuggling occurred in around 8 percent of them. It’s believed that the research team shall also come out with the complete dataset as well as the measurement pipeline browser developers can refer to.

Raising Awareness about UID Smuggling

The first author, a computer science student pursuing a Ph.D. at UC San Diego, Audrey Randall, states that the primary intention of their mission was to make browser developers aware of the menace of UID smuggling.

She reveals that while it’s yet to be known how much of a threat UID smuggling is to user privacy, the fact remains that it’s used more widely than the researchers had initially anticipated.

The researchers point out that there can be legitimate uses for UID smuggling. Websites can know if a user is already logged in, so the users can skip the login page and move on to the content right away when user IDs are embedded in URLs.

Companies owning websites with separate domains can use UID smuggling to track user traffic. Affiliate advertisers can also use it to gauge website traffic, so they get paid for their efforts. Bloggers who are into affiliate marketing use links that surfers may click on, which results in a commission for them. UID smuggling helps locate the blogger who should receive the commission.

The Dangers Posed by UID Smuggling

What the researchers are worried about is the potential of UID smuggling being used for harmful purposes. Data brokers could use it to create a database with the internet navigation details of various users.

There was another small exercise carried out by the researchers. UID smuggling was manually blocked for multiple navigations. It was found that the impact on a website’s functionality was only negligible. As a next step in the fight against UID smuggling, a tool could be built that will block UIDs. However, the researchers caution that it would be no more than only a mere step in what is essentially a game of being a step ahead of UID smuggling.

How to be More Private

What we, the common users of the internet, should worry about is the threat UID smuggling poses to our privacy. Once advertisers get to know which sites we visit, they get to work and create a profile of ours. That leaves us as sitting ducks before the menace of targeted advertising. Besides, UID smuggling reveals details of our online surfing behavior, something that we would prefer to remain under wraps.

All of us realize how important it is to keep our surfing history private. UID smuggling has made it clear that merely using browsers that block third-party cookies doesn’t help.

So, you should try to be as private and anonymous as possible. Getting a VPN for PC is one way to combat entities tracking your computer. A Virtual Private Network connects you to the internet using remote servers, which keeps your online actions hidden. Essentially, the server makes online requests on your behalf. Since the internet traffic also gets encrypted, it becomes far more unlikely that someone can snoop on you.


The fight against online tracking won’t conclude until a solution is found that helps the ad industry to generate profits with individual online privacy not being compromised either. So, one reason why Google delays its cookie elimination is that it cannot find suitable alternatives. While it is essential to find balance, users’ comfort and privacy should be considered top priorities.


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