McAfee researchers have discovered various Google Chrome extensions that steal browsing activity, with the add-ons racking up more than a million downloads.

As reported by Bleeping Computer, threat analysts at the digital security company have come across a total of five such malicious extensions.

With more than 1.4 million downloads, the extensions have tricked an unprecedented number of individuals into adding them to their browsers. The extensions in question that have been tracked down thus far are:

Once one of the extensions listed above has been installed onto Chrome, it can subsequently detect and observe when the user opens an e-commerce website on their browser. The cookie that is generated by the visitor is altered in order to make it seem they arrived at the site via a referrer link. Ultimately, whoever is behind the extensions can then receive an affiliate fee should the target buy anything from these sites.

All the extensions actually deliver on whatever functionality is listed on their Chrome web store pages. Coupled with the fact that they showcase a user base in the tens or hundreds of thousands, it may convince many that they’re safe to download if they’re being utilized by so many individuals.

While the Netflix Party extensions have been taken down, the screenshot and price tracker ones are still live on the Chrome web store.

As for how the extensions work, McAfee detailed how the web app manifest — an element controlling how the add-ons run on the browser — executes a multifunctional script, allowing browsing data to be sent directly to the attackers through a certain domain that they’ve registered.

Once a user visits a new URL, their browsing data is sent with the use of POST requests. Such information includes the website address itself (in base64 form), the user ID, device location (country, city, and zip code), and a referral URL that’s encoded.

To avoid being detected, some of the extensions won’t activate their malicious tracking activity until 15 days after it’s been installed by the target. Similarly, we’ve recently seen how threat actors delay their malware being loaded onto a system for up to a month.

Hackers have increasingly relied on hiding malicious codes and malware in free Windows software and downloads. Most recently, they’ve been targeting users with space images, as well as trying to breach systems via Windows Calculator.