Bay Area rapper Saweetie didn’t intend for “My Type” to come out as a single. But when a clip of the bouncy anthem about desirable (and slightly vulgar) attributes in a partner started to take off on TikTok as part of a social media challenge, it became clear the song would be her defining hit.

The racy rap is now the backdrop to countless 15-second videos of people posting their own tongue-in-cheek lists of partner preferences. With more than half a billion views and counting, the #MyType hashtag on TikTok has put Saweetie on the map as a breakout star, sending the song platinum and making it a Top 40 pop radio hit. 

“TikTok is changing the way music is discovered,” says Saweetie’s manager, Max Gousse, founder of Artistry Records. “We’re able to take this discovery and build it into a music marketing campaign that yields real sales.” 

Initially brushed off as a tween phenomenon, TikTok has in the past year risen to become a sort of second coming of Vine, with a unique musical twist, and is turning into a serious rival to Facebook, Instagram and YouTube. The app has now surpassed 1.5 billion downloads worldwide, half of them in just the past year. Its owner, Chinese artificial intelligence firm ByteDance, is one of the world’s most valuable startups, with a valuation of $75 billion, and one of the few Chinese tech companies not at least partially owned by Alibaba or Tencent. It’s reportedly eying a Hong Kong IPO next year.

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With explosive growth, however, have come serious questions. As the first Chinese-owned social media platform to become the most downloaded app in the U.S., TikTok is under intense scrutiny over how it stores personal user data and whether it censors content Beijing doesn’t like. Evidence that ByteDance is involved in pushing propaganda related to China’s crackdown on Muslims in its northwestern Xinjiang region could also give Americans pause. 

Last week, news broke that TikTok has been hit with a class action lawsuit filed in California that claims the company “clandestinely … vacuumed up and transferred to servers in China vast quantities of private and personally identifiable user data.” It also says Chinese code discovered in 2017 to enable developers to install spyware was embedded in the app.

The suit comes even as a secretive U.S. government body called the Committee on Foreign Investment in the United States is conducting a national security probe into ByteDance’s $1 billion acquisition in late 2017 of the Shanghai-based lip-syncing app Musical.ly, which it rebranded as TikTok. Last year, the committee blocked a Chinese firm from acquiring payment service MoneyGram and ordered another to sell gay dating app Grindr over similar data security concerns.

Even if TikTok is mostly full of silly dance routines, “any platform owned by a company in China which collects massive amounts of data on Americans is a potential serious threat to our country,” Sen. Marco Rubio, R-Fla., recently tweeted.

TikTok did not respond to requests from Variety for comment.

Company chief Alex Zhu has tried to allay fears over the app, saying that its global data is stored in Virginia, with a backup server in Singapore, and is segregated from the rest of ByteDance. Even if Chinese president Xi Jinping himself asked the firm to hand over user data, it wouldn’t do so, Zhu says.

But many China experts describe his statements as misleading, since most, if not all, of the ByteDance engineers working on TikTok are thought to be based in Beijing, meaning that even data held outside China is flowing into the country so that the app can be updated and improved. Chinese cybersecurity law also dictates that local firms must share data with the state upon request.

After Chinese authorities took down ByteDance’s popular comedy app Neihan Duanzi last year because of content they deemed vulgar, ByteDance CEO Zhang Yiming issued a groveling apology for allowing algorithms rather than “core socialist values” to determine content, and vowed to increase his staff of censors from 6,000 to 10,000, favoring recruits with “strong political sensitivity.” Months later, Zhang was chosen as one of China’s 100 “outstanding private entrepreneurs” who “resolutely uphold the [Communist] Party’s leadership,” an award heavily determined by the government agency that handles Chinese influence operations abroad.

Separately, ByteDance was found in violation of U.S. child privacy laws last February and had to shell out $5.7 million for knowingly allowing underage kids on its platform.

None of this has driven Americans away from TikTok. About 60% of the app’s 26.5 million monthly active users in the U.S. are between the ages of 16 and 24. “Advertisers and brands must incorporate TikTok into their strategies today in order to succeed tomorrow” with Generation Z, even if it isn’t generating immediate returns yet, says David Neuman, director of social media and sales strategy at digital advertising company RhythmOne.

TikTok’s ballooning influence is evident in the number of celebrities creating accounts, with Reese Witherspoon, Will Smith and Dwayne “The Rock” Johnson coming on board in the past three months. It’s also visible in the growing list of new artists the app has managed to mint — most visibly, Lil Nas X, who burst onto the scene after his country-rap hybrid “Old Town Road” went viral on TikTok and eventually became the longest-running No. 1 song in U.S. chart history. He’s now up for six Grammys, including album and new artist.

TikTok videos average 15 seconds, compared with 11 minutes, 42 seconds, for YouTube, meaning that TikTok users can consume nearly 50 pieces of content in the time it takes a YouTuber to watch one. With easy-to-learn editing tools, TikTok also makes it simple for users to create and react to content, which encourages buy-in, says Dan Levin, president and co-founder of video advertising platform ViralGains.

Now that Instagram’s audience is skewing older and YouTube is chasing marketing dollars by focusing on top-tier creators, TikTok fills a gap for low-production-value content where people appear authentic. Paid ads remain limited, with most revenue coming in for the platform and creators via the online payment practice of virtual gifting. 

The main lure of the app is its promise of instant fame. It’s almost impossible to become as big as Kylie Jenner on Instagram or Twitter these days for a nobody starting from scratch. The TikTok algorithm is more democratic, filling its stream of user-personalized content with videos from totally unknown accounts alongside those from the most-followed creators. 

But that algorithm has a potential dark side. The company has enormous sway over what goes viral and what doesn’t, and its decisions lack transparency, which is problematic if it’s the Chinese government indirectly calling the shots.

The degree to which TikTok is censoring its U.S. content is contested. Leaked documents show that TikTok tries to keep politics off its platform, and has explicitly banned topics disagreeable to Beijing such as the Tiananmen Square massacre, Tibetan independence and the outlawed religious group Falun Gong. It also has the ability to enact “shadow bans,” leaving videos up but algorithmically downplaying them or blocking them from search results so that they’re not seen by users — a type of censorship much harder to notice or prove.  

The issue made headlines recently when 17-year-old American Feroza Aziz put out a clever video that began as an innocuous makeup tutorial but quickly morphed into a discussion of alleged Chinese human rights violations in Xinjiang, where more than a million Muslim Uighurs are believed to be held in detention camps.

Aziz’s TikTok account was temporarily suspended, and her viral video was removed for about an hour. Both her account and the video were reinstated after a media blitz about the incident. The company has attributed removal of the video to “human moderation error,” which some China watchers say indicates that TikTok and the Chinese version of the app, Douyin, are being monitored by the same censors. Another analysis shows that TikTok reviews videos in patterns similar to those of Douyin.

The takedown of Aziz’s video came days before publication of a report by an Australian think tank that named Byte-Dance among Chinese tech firms “engaged in deeply unethical behavior in Xinjiang, where their work directly supports and enables mass human rights abuses.” Douyin is actively working with Chinese internet and public security authorities to boost the Xin-jiang police force’s “influence and credibility,” among other initiatives, the report says.

Such news comes as no surprise to researchers such as Yaqiu Wang of Human Rights Watch. “We all know that Chinese companies all ultimately have to answer not just to their investors but to the Chinese Communist Party,” she says. “But if Byte-Dance wants to be international, they’ll have to start caring not only about what they’re doing with TikTok outside of China but also about what they’re doing with other parts of their company inside China.”

While it might be second nature for a Chinese company to avoid politics, Byte-Dance will have to solve its censorship conundrum to become a truly global player, Wang says. “You can’t be an international company that says, ‘We don’t talk about politics, period.’ That’s just not how the world operates. In countries that have free speech, people are political and want to use platforms to express their political views.” 

TikTok may be the first Chinese app to make it big in the U.S., but it likely won’t be the last. ByteDance and future tech firms that follow in its footsteps will have to tread carefully on free-speech issues if they don’t want American users to decide that this kind of restrictive social network isn’t, as Saweetie might say, “My Type” after all.