Like Snapchat's gender swap and FaceApp before it, mobile application Zao has become something of an overnight sensation. But, not solely for the right reasons.

So, what is Zao? How can you get it? What does it do? And, why has it set the internet alight?

We answer these questions and more below.

What is Zao?

Like several other recent apps and Snapchat lenses, Zao is a face-swapping iPhone application that has gone viral almost overnight.

Originating in China, it came out on 30 August and soared straight to the top of the Chinese App Store chart as the top free download in the country.

Unlike other face-swapping apps, it uses deepfake technology to replace the faces of celebrities and film stars in video clips with your own. Examples online show some very impressive results.

However, it has not come without controversy. As with most Chinese software and hardware these days, privacy concerns have been voiced.

As reported by Bloomberg, a previous version of the app's terms and conditions stated that developer Changsha Shenduronghe Network Technology (a subsidiary of Momo Inc) would retain "free, irrevocable, permanent, transferable, and relicense-able" rights to any images of yourself you upload.

After a public outcry, the T&Cs were altered, with the studio now claiming that it won't use your pictures or mini-videos for anything other than to improve the app or uses pre-agreed with you. And, if you delete your uploaded content, Momo says that it is committed to deleting it from its servers too.

The new stance hasn't changed the App Store rating, with thousands of negative reviews having flooded Apple's digital service, but if the trend with other similarly concerning apps is anything to go by, the general public won't really care. They'll use Zao regardless.

How to download and use Zao

Zao is available on Apple App Stores around the world, for iOS devices and found through the App Store on your iPhone or iPad. However, it is currently only available in the Chinese language and, even with privacy concerns shelved, it is almost impossible to navigate around its many screens without being fluent in the language.

It also requires your phone number to log in (reports Reuters), so it is unlikely that you will be able to register an account until a full, global version becomes available.

In fact, until there is an English version of the application, we wouldn't suggest you try to use it anyway, as all the terms and conditions are in Chinese and you might not know what rights you are signing away.

How Zao works

Zao uses deepfake artificially intelligent earning to assess uploaded images of your face in order to accurately place them on actors in movie clips.

If you upload several images, including shots of you blinking or opening your mouth, the end result will be even more realistic.

Basically, the software analyses the positioning and facial expressions used in the video clips and recreates them using the digital information gleaned from your facial images.

The privacy concerns are that the photos you upload can then be used by the main company for other means. The same happened with Russian mobile application FaceApp.

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