Apps like Yelp ($YELP) and TripAdvisor ($TRIP) allow users to login via Facebook credentials for a quick and seamless experience. This not only allows for a simper user experience for users, keeping them logged in whenever they need a quick restaurant or hotel recommendation, but it also allows app makers to track usage data to help improve their apps.

As we've learned this year, it also means app makers can potentially sell that data to others who are looking to profile Facebook users. After Cambridge Analytica was caught using data gleaned from apps for nefarious political purposes, Facebook changed its data-collection policies for app makers. According to our data, some apps were affected more than others, indicating that some were tracking more than they should have.

Here's how we know: Facebook tracks login usage in order to rank apps by popularity. It's a simple, useful way to track which apps are most popular and which ones are being used the most.

Yelp, which has been a top-30 app on Facebook since 2016, dropped by more than 300% in April 2018 after the new policies.

On April 8, 2018, Yelp was the 28th-most popular app according to Facebook monthly login rank data. As of today, it's slipped to 88th place, the lowest it's been since we began tracking Yelp's rank in July, 2015.

Normally, this is a sign of one of two things: either the app removed Facebook login or the app is simple being used less.

As of today, users can still login via Facebook on the Yelp app and website.

Such a change — especially a drop like this — can also be a sign of a database error in which our Thinknum bots are pointed in the wrong direction while a newer version of the app should be tracked instead. In this case, though, the Yelp app has kept its same name. Around the time of the drop, however, Yelp did publish a new version of its app on April 9, 2018. Version 12.8.0 has the following bizarre update info:

"Due to a typo in the previous version's code, Yelp briefly became self-aware. We've fixed that along with a few other bugs. Please disregard any poetic, philosophical, and/or menacing messages you received from the app recently."

Around the same time, TripAdvisor saw an even more precipitous drop:

As recently as April 10, 2018, TripAdvisor was a top-10 app on Facebook. As of today, it's sunk to spot 82.

To be clear, not all apps were affected by the Facebook policy changes. For instance, dating app Tinder continues to do well:

The affected apps, Yelp and TripAdvisor included, appear to have been hit by login token changes that Facebook made in April in the shadow of the Cambridge Analytica personal data controversy.

It's unclear if the apps in question were collecting private data beyond the comfort zone of Facebook, or if the apps were keeping users logged in longer than they should to pad their usage numbers (and potentially collect usage activity in the meantime). What is clear, however, is that the new policies have hurt their usage rankings on Facebook.

We reached out to Yelp for comment and haven't heard back yet. We'll update when we have.

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