A mysterious Kardashian-endorsed selfie app exploded onto the App Store charts last week. Now,very nice couple having sex video users are complaining about big credit card charges — and shady imposters are vying for a piece of the action.

If you’re not already familiar, the app is called Gradient, and it's been dominating social media thanks to its celebrity "look like" feature, which compares your selfies to photos of celebrities.

The app quickly achieved viral meme status thanks to endorsements from the Kardashian clan and other celebrities who've eagerly shared their own celeb doppelgängers.

But you might want to think twice before you download it.

What is Gradient?

The photo-editing app boasts various "AI"-powered capabilities. But the feature that's received the most attention is its "look like" function, which takes your selfies and compares them to images of celebrities to tell you which famous person you "look like." It then arranges a series of images into a shareable collage.

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The app launched in September of this year, but wasn't widely downloaded until several members of the Kardashian clan began promoting it on their Instagram Stories. Around Oct. 15, Kim Kardashian, Kourtney Kardashian, Khloe Kardashian, Kylie Jenner, and Scott Disick all posted screenshots from the app to their Instagram Stories, according to The Sun, which noted at the time that all the posts were tagged with #ad, indicating they had been paid to promote the app.

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Regardless, their stamp of approval sparked a massive wave of downloads. Prior to its celebrity endorsement, the app had never ranked higher than the No. 541 spot in any one category, according to data from analytics firm Sensor Tower. Just days after the Kardashian plug, the app was No. 1, with more than 8 million downloads in the App Store and Google Play.

Who is Ticket to the Moon?

The app's sharp rise also raised questions about the app's origins. Its developer, called "Ticket to the Moon, Inc.," has not released any other apps, and there's very little information about the company online.

A number of articles have noted that a Delaware address listed on the company's terms of service is actually an address for a private equity investment firm called Meihua Capital Partners. When Mashable viewed the app's terms of service on Friday, it listed the Las Vegas address of a virtual office services company called MyCompanyWorks.

MyCompanyWorks confirmed Ticket to the Moon is a client, but didn't provide further information about the company. Messages Meihua Capital Partners have not been returned.

In an email, a Gradient representative told Mashable Ticket to the Moon was founded by Vladyslav Urazov and Bogdan Matveev, who previously sold their startup, Teleport, to Snap in 2018.

Some people have also noted that Gradient's privacy policy leaves open the possibility that users' data can be used for other purposes, including advertising or the creation of "other new products and features."

"We do not collect or store images and Face Data and we do not transfer it to third parties," a Gradient spokesperson said. "A simple traffic analysis of our app can prove the fact that no private data is sent, including images and Face Data. This data never leaves the app, it stays private and is fully owned by the user."

If these concerns sound familiar, though, then it's likely because the situation bears many similarities to the controversy over FaceApp, the selfie app that went viral thanks to its age filters. After that app went viral this summer, there was an almost immediate backlash after conspiracy theories spread about the app's supposed Russian origins. (The app's founder is Russian, but has said the company doesn't store data there, and multiple security researchers uncovered no evidence the app was misusing data.)

But while FaceApp's founder immediately answered questions about his app, "Ticket to the Moon" has been less forthcoming. The app has a basic website, but few social media accounts (Gradient appears to have an Instagram account), and no contact information other than a generic email address. And the only physical addresses linked to the company have been the virtual office services firm and Meihua Capital Partners, which also has a notably small internet footprint.

Of course, none of these things on their own prove anything about Gradient's origins or what its motivations are, though they are certainly cause for some caution. There is, however, a much simpler reason you should avoid Gradient.

It's all about the $$$$

The app appears to be using its current No. 1 status to get users to buy an expensive, automatically renewing subscription.

That's because, upon downloading the app, users are prompted to agree to a three-day "free trial" in order to try the lookalike feature. What might be less clear to some users is that after that three-day window is over, you'll be opted into an automatically renewing $19.99 monthly subscription.

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A quick look around Twitter shows that a number of unsuspecting users are already upset with the app for charging them for the full monthly "premium" subscription." So far Gradient has grossed more than $1.1 million in the App Store and Google Play, according to Sensor Tower, and those numbers are likely to rise as more "free trials" end.

While the app offers other features besides the selfie comparisons, it does appear to be something of a cash grab. A closer look at the app's subscription offerings also show a $3.99/month subscription, though that's not the default offered on the sign-up page.

And, it's not just Gradient you have to worry about. As we saw with FaceApp, shameless clones of Gradient are also going viral. An app called "Look Like You? Celebrity!" was briefly No. 2 in the App Store, despite appearing to break Apple's developer guidelines which prohibit copycat apps. The app made at least $9,500 from users before the app was removed.

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And, at the time of this writing, an app called "My Replica - Celebrity Look Like Me" appears to capitalizing on the "celebrity lookalike" trend even more shamelessly. Upon downloading the app, it prompts you to buy a "diamond subscription," which costs $99.99 a quarterafter a three-day "free trial." That app has raked in more than $363,000 in the month of October alone, according to Sensor Tower.

These types of schemes are against Apple's rules, but the company has continued to struggle with rooting out these apps, which come up with unique ways to game search results in the App Store.

So between copycat apps trying to scam you, the actualapp trying to scam you into a subscription you probably don't want, and very real questions about the app's origins and motivations, you should probably stay away from Gradient and other apps like it, no matter how appealing those celebrity "lookalike" screenshots are.

UPDATE: Oct. 22, 2019, 11:39 a.m. PDT This story has been updated with more information about Ticket to the Moon.