UC Browser for Android appears to have been taken down from the Google Play Store. The mobile-friendly version of the web browser seemingly disappeared without a trace earlier today, just weeks after the app topped 500 million downloads on Google’s mobile store.

For those unfamiliar with the name, UC Browser is developed by UCWeb, which is owned by China’s Alibaba Group. As well as being a hugely popular alternative to Google Chrome in its home region, UC Browser has an enormous base in India.

While Chrome has since reinstated some of its dominance, back in June, UC Browser became India’s favourite mobile browser and at one point grasped over 50 percent market share. In addition, it is the sixth most downloaded Android app in India.

UCWeb has also claimed that Indian users make up 100 million of its total monthly active users from around the world, with the latter figure reportedly reaching 420 million, per reports from 2016. As a result, its removal is a shocking step to say the least. It will also lead to a number of key questions, most notably: why was it removed after all this time and after so many downloads?

UC Browser’s disappearance was first spotted by the eagle-eyed netizens on Reddit, and its users have an interesting theory.

Chrome is the most popular browser in the world, both on desktops and mobile devices. To keep it running as fast and smooth as possible, it’s always a good idea to have the latest version …

Reports began swirling in August that claimed UC Browser has a rather nasty habit of stealing sensitive user data which it then sends back to remote servers in China without the user’s consent. As part of a widespread investigation into data security, Indian government officials expressed concerns that the UC Browser app continues to collect this data after it has been uninstalled, per a Times of India report.

UC Browser has come under scrutiny regarding data security concerns in the past. In 2015, Canadian researchers claimed that the Chinese and English-language version of UC Browser “made easily available to third parties personally identifiable information like location, search details and mobile subscriber and device numbers.”

Many of the Reddit posters addressing UC Browser’s unexpected disappearance seem to think that the recent allegations are to blame, as it had been thought that the app could be banned in India should the accusations hold any water.

At present there is no evidence to either confirm or deny these suspicions and both Google and UCWeb are yet to comment on the situation, at the time of writing. UCWeb has previously denied any wrongdoing, stating that it “will not do anything to breach the trust of our users” and that it takes “security and privacy very seriously.”

There’s certainly more to this story and we’ll be keeping an eye out for any official word on the matter. In the meantime, it’s worth noting that the UC Browser Mini, an alternative app built for less powerful devices, is still live on the Play Store.