Selling user data to third parties is a common practice for many apps, but it is often predicated on the assurance that the software or service provider will properly anonymize the personal data it collects before making a profit. According to The Hacker News, however, popular Chrome and Firefox extension Web of Trust (WoT) dropped the ball. Here’s what the WoT privacy breach means for end users.

Web of Treachery

Since 2007, WoT has promised users a “safe web search and browsing” experience, The Hacker News reported. It uses crowdsourcing to rate websites for overall trustworthiness and child safety. Seems like a noble goal, right?

But the app has also been collecting data about its users, including account names, mailing addresses and browsing history. Before selling this data to third parties, per the user agreement, the company was supposed to scrub it clean of any identifying details.

As noted by Lifehacker, however, an investigation by German television channel NDR found it was possible to match supposedly anonymous data to individual users. What’s more, with access to browser history, NDR was able to determine users’ travel plans, shopping habits, general medical histories and even sexual preferences.

While the report only used 50 WoT user accounts to demonstrate the vulnerability, it was damning enough for Mozilla to remove the extension from its add-on page. WoT then removed its own extension from the Chrome Web Store and promised to correct the issues by properly “cleaning” user data.

Read the Fine Print

With more than 140 million users worldwide, the WoT privacy breach is a big deal, and not just because private user data was up for grabs. The failure also speaks to the commonplace nature of third-party data selling.

Individual and business consumers alike typically click through user agreements without reading the fine print, often granting apps and extensions permission to sell their data and access portions of their device that aren’t necessary for new software to function, like user locations or contact list data.

As noted by CNBC, governments are taking some steps to curb this problem. Internet providers will now be on the hook for obtain “explicit” consent from subscribers before selling their data to third parties. While this doesn’t yet apply to app-makers and service providers, it’s a step in the right direction.

WoT Privacy Breach Highlights Risks

It’s also worth noting the business-level implications of the WoT privacy breach. With so many corporate employees now using mobile devices that pull double duty as personal and business online portals, it’s a safe bet that WoT and similar programs are commonly installed. With identifiable data easily matched to user profiles, corporate data could be at risk, especially if users are accessing company web portals over insecure connections and using stock login/password combinations.

WoT’s breach may not have been malicious, but it remains worrisome. Trust is a rare commodity online. Now companies must double down on cybersecurity diligence to avoid unwanted exposure.

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