In January 2017, Justin Hindman announced that Stylish, a popular open-source web browser extension he had created that allows users to apply any style sheet (CSS) to any web page, had been acquired by web analytics and market research company, SimilarWeb. It has now been revealed that SimilarWeb has been using the browser extension's extensive permissions to collect users' web browsing history.

What's interesting is that before Stylish was acquired by SimilarWeb, users were not required to create an account but this all changed in January 2017 along with other creepy "features" that users were not alerted to.

"Unfortunately, since January 2017, Stylish has been augmented with bonus spyware that records every single website that I and its 2 million other users visit. Stylish sends our complete browsing activity back to its servers, together with a unique identifier. This allows it’s new owner, SimilarWeb, to connect all of an individual’s actions into a single profile. And for users like me who have created a Stylish account on, this unique identifier can easily be linked to a login cookie. This means that not only does SimilarWeb own a copy of our complete browsing histories, they also own enough other data to theoretically tie these histories to email addresses and real-world identities," explained Robert Heaton on his blog after making the discovery earlier in July 2018.

With that said, it's important to highlight that this was not"hidden" as it was public knowledge since SimilarWeb acquired Stylish in 2017. In fact, Hindman also explained that users could opt-out of "data collection" although this would mean that certain Stylish features would not be available. However, the fact that it is enabled by default raises concerns about SimilarWeb's intentions.

SimilarWeb have since explained that they collect browsing history in order to use that data to recommend style sheets to Stylish users. Quite a flimsy excuse especially when you also consider that as part of this "surveillance" feature, Stylish now also scrapes and stores users' Google searchea.

How all this feeds into SimilarWeb's business model is up for speculation, but considering that they are a data analytics and Internet market research company, it's probably a good guess that the user data, approximately 2 million Stylish users, collected feeds into informing the paid analytics service they provide to customers.

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