TikTok, the short-video sensation that’s among the world’s most downloaded apps, is coming under increased scrutiny about its data security as it guards the personal information of over a billion users.

On Monday, several cybersecurity analysts tweeted about the discovery of what was purportedly a breach of an insecure server that allowed access to TikTok’s storage, which they believe contained personal user data. Only days earlier, Microsoft Corp. said it had found a "high-severity vulnerability” in TikTok’s Android application, "which would have allowed attackers to compromise users’ accounts with a single click.”

ByteDance Ltd.’s TikTok surpassed a billion monthly users a year ago and now ranks as many young people’s favorite app. That makes it an enticing target for hackers who may seek to hijack popular accounts or resell sensitive information. It was identified as a privacy threat by the administration of then-U.S. President Donald Trump in 2020 and nearly banned because of concern about potential links between its Beijing-based parent company and the Chinese government.