A new mobile app, sarahah, topped the free download apps list of the Google Play Store and the U.S. App Store of Apple. Teenagers from the U.S. and other countries drove the relatively unknown anonymous messaging service to the top of rankings as the most-downloaded app.

On iPhone, Sarahah got more than 3.9 million downloads and on Android over 1 million downloads at the start of this week. The additional users boosted the total registered users to 15 million, while visitors reached 130 million in the past month. The U.S. topped the app’s biggest market with 76 million unique visitors, followed by the UK at 16 million.

Zain al-Abidin Tawfiq, a developer from Saudi Arabia, launched Sarahah in 2016 as a website where employees could provide anonymous and honest feedback to their employers. Sarahah is an Arabian word for “honesty,” according to Financial Times. It initially gained wide use in Arabic-speaking nations. After Tawfiq came up with an English version of the website, it caught fast with teens in different parts of the world, Fortune reported.

Discovering strengths and areas for improvements

Since Tawfiq developed Sarahah as a tool for employers to receive honest feedback from their workers, the app encourages users to write a constructive message and to pick a recipient. The app has a filter that permits the user some control who could send them a message which could be labeled as a “favorite” message.

Besides not allowing the recipient of the anonymous message to reply, the website assured senders they will remain unknown to the receiver of the message unless consent is given. To sign up for an account, netizens could go to the Sarahah website, while the Messaging App can be downloaded on mobile devices that run on iOS or Android.

Tawfiq said the messaging app aimed to break some barriers between people that prevent them from giving feedback. It could be age or position. “You can’t go to someone who is a grandfather and tell them everything you think about them,” the developer explained.

The anonymous nature of the feedback, however, opens Sarahah to be used by cyber bullies due to lack of consequences for the messages they send.

Racist messages and other forms of harassment have been reported in app store reviews. The messages often are either really nice or really mean. Some users got indecent proposals, while one user wrote in an App Store review that a school friend died, but one texter commented the victim deserved to die.

One billion users for WhatsApp

Meanwhile, WhatsApp reported that users of the very popular messaging app have increased to 1 billion from every month to every day to keep in touch with family and friends. The communication could be through personalized videos and photos, video calls, and updates using the app’s Status feature.

The active monthly users have increased to 1.3 billion people who send 55 billion messages per day. Photos sent are 4.5 billion daily, and videos at 1 billion a day. The app supports 60 languages.