【Watch Ava Online】

Chinese face-swapping app Zao has blown up within days of launching,Watch Ava Online however, not without widespread concerns over privacy.

Allowing users to create an almost instant deepfake using their own face in place of a celebrity's, the app — created by social media platform developer Momo Inc. — has become incredibly popular since launching on Friday.

According to the South China Morning Post, posts with the hashtag #zao have seen more than 8 million views on Weibo, China’s version of Twitter. And as Bloomberg reports, Zao is currently sitting at the top of China's iOS store in the free download section, hitting the top by Sunday.

How does it work? Incredibly and scarily easily. Users simply upload a selfie to the app, which will drop their face onto that of famous movie stars like Leonardo DiCaprio, Sheldon from The Big Bang Theory, or John Bradley from Game of Thrones. You can only upload your face into particular movie and TV scenes available in the app — you can't just add someone's face into, say, a crime scene or a political moment.

Twitter user Allan Xia tried the app, taking over DiCaprio's face in scenes from films such as Titanicand Baz Lurhmann's Romeo + Juliet, and more, all reportedly generated within eight seconds.

And it's pretty effective.

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Twitter user Matthew Brennan tried their face on Sheldon's, and though it's not as effective as the above, it only took a few seconds to make.

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And here's Twitter user Sam Driver-Tweddell as Samwell Tarly from Game of Thrones.

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Zao's popularity and dalliance into deepfakery comes with inevitable privacy concerns, however. This particularly applies to the photo uploads, as Bloomberg notes, users can either add an existing photo of themselves, or take new ones using the app — these include images of you blinking to assist with the realism of the deepfake rendering.

According to the publisher, which observed a now-adjusted version of Zao's user agreement, the company claimed "free, irrevocable, permanent, transferable, and relicense-able” rights to any content uploaded to the app.

Users reportedly flooded the App Store with negative reviews, as Bloomberg reports Zao's rating as 1.9 stars out of five, with over 4,000 reviews, many citing privacy as an issue.

Mashable has reached out to Apple for comment.

The publisher reports that Zao has now updated this, saying that any selfies or videos added to the app won't be used for anything other than app improvement or anything other than what the user has previously agreed to.

Importantly, the app reportedly said any content deleted by users will be erased from Zao's servers, though this seems too good to be true.

“We understand the concern about privacy. We’ve received the feedback, and will fix the issues that we didn’t take into consideration, which will need a bit of time,” reads a statement posted to Zao’s Weibo account.

Chinese messaging platform WeChat blocked all content shared from Zao on Monday.

People are right to be concerned over privacy with face-swapping and deepfake-generating apps. Recently viral platform FaceApp, which allowed people to see themselves as older or as another gender, faced backlash thanks to its problematic privacy policy — among other things.

There's also general concern over deepfakes themselves. Although they can be pretty neat (like that Bill Hader/Tom Cruise vid) they're getting undeniably scarier as deepfake technology gets better — and with Zao, faster. Harmful disinformation spreads like wildfire, and if a viral app can efficiently fan those flames, we're in trouble.