The Logo of social media app TikTok (also known as Douyin) is displayed on a smartphone on December 14, 2018 in Berlin, Germany. Thomas Trutschel | Photothek | Getty Images

Popular Chinese video sharing app TikTok is under investigation in the U.K. for how it collects and uses children's personal information. Elizabeth Denham, head of the U.K.'s Information Commissioner's Office (ICO), said in a parliamentary hearing Tuesday the agency is investigating whether TikTok violated the EU's data privacy law called GDPR (General Data Protection Regulation), which requires companies to provide specific protections related to children's personal data. "We are looking at the transparency tools for children," Denham said. "We're looking at the messaging system, which is completely open, we're looking at the kind of videos that are collected and shared by children online. So we do have an active investigation into TikTok right now, so you can watch that space."

TikTok, owned by Chinese private company ByteDance, lets users create and share short videos and pair them with music and other special effects. The app had 500 million monthly active users as of February and was the third-most downloaded app in Apple's App Store and Google Play combined in the first quarter of the year, according to research firm Sensor Tower. TikTok, which was formerly known as Musical.ly and goes by the name Douyin in China, is especially popular among teenagers and preteens. This has raised eyebrows among some regulators worried about the privacy of minors online, including the U.S. Federal Trade Commission (FTC). In February, the FTC fined TikTok $5.7 million for illegally collecting children's personal information. The agency said the app failed to notify parents that it gathered and used the personal data of users under the age of 13. The FTC also warned that strangers could send direct messages to users with private accounts, adding "there have been public reports of adults trying to contact children via the Musical.ly app."