FaceApp is currently the most popular free app on Google Play and Apple's App Store.
More than 100 million people have downloaded the app from Google Play.
It is the top-ranked app on the iOS App Store in 121 countries.
It is essentially a selfie-editing tool that utilises filters to change the way one looks.
Its current most popular filter allows users to age photos of themselves.
Countless casual users and celebrities have jumped onto the trend.
But there are mounting concerns with how FaceApp handles user data.
When was FaceApp first popular?
FaceApp first became popular in 2017.
It uses artificial intelligence to alter people's faces to see how they would look with different hair colour, eye colour or as a different gender.
How does FaceApp function?
Photos added to FaceApp are uploaded to a server for processing before being sent back to the user.
This is different from uploading a photo onto the app on the phone, which is localised.
What does FaceApp's terms of service grant the company?
FaceApp's terms of service give the company licence to use photos and other information uploaded by users for commercial purposes, including their names, likenesses, and voices.
FaceApp may continue to store user data after it is deleted from the app.
There is no limitation on how long the data can be kept.
Where was FaceApp developed?
What are the implications for users?
User photos and app data can be stored in Russia, the country where the app's development team is based.
All information collected by the app can be stored and transferred to whichever countries FaceApp and its affiliates operate from.
However, FaceApp said it is using Google and Amazon-owned servers in the United States.
Why does FaceApp store photos on the server?
FaceApp says photos stored on the server are kept to make the editing process more efficient for its users and that the photos are usually deleted within two days.
The company says user data remains on the server side and not transferred.
FaceApp said 99 percent of users choose not to log in, so they don't have much in the way of identifying information.
The company said it also accepted user requests to remove all personal data from their servers.
But its support team was backlogged with those requests.
What assurance did FaceApp give various international media?
FaceApp's statement said they wouldn't sell data to third-party companies and that data was not being transferred to Russia.
But according to FaceApp’s terms of service, when you use the app you grant it a “perpetual, irrevocable, nonexclusive, royalty-free, worldwide” license to do whatever it wants with your photos.
Is it true that FaceApp has access to all your photos on your phone?
Security experts have not detected any unusual practices with the current version of FaceApp.
iPhone users, for example, can block FaceApp and other apps from viewing their full photo libraries through the iPhone's settings.
There is no evidence FaceApp has access to all your photos.
Forbes reported that FaceApp now has 150 million users' faces and names.