With more than 1 billion monthly users worldwide, TikTok has transfixed many users with a platform that seems to know who they are. But critics say TikTok might know too much.

The popular social media app tracks its users' likes, dislikes and personal information, including email addresses, phone numbers and WiFi networks.

Gizmodo senior technology reporter Thomas Germain showed CBS News how TikTok sweeps up user data, including access to users' contacts.

"They're looking through all of my contacts to see whether those people are on TikTok, but who knows what they're doing with it," Germain said. "They're definitely keeping track of everything that's in there, whether those people are on TikTok or not. And the interesting thing there is my friends didn't consent to having their phone numbers and emails uploaded in TikTok."

While other apps also take similar data, TikTok's parent company is Chinese-owned ByteDance, and U.S. officials have repeatedly warned that the Chinese government could force the company to share the data it collects on its users.

"We do have national security concerns," FBI Director Christopher Wray said in November. "They include the possibility that the Chinese government could use it to control data collection on millions of users."

A growing number of states and the U.S. military have banned the use of TikTok on government-issued devices because of those fears.

John Carlin, who previously ran the Justice Department's National Security Division, said the collected data can be very valuable.

"We think about data itself — people have called it the new oil," Carlin said.

He worries Chinese officials could also influence what videos are shown to Americans.

"It's not just the collection or theft of that data," Carlin said. "It's also manipulating what it is that you see. And the question is for the national security professionals, do we want China determining what it is that we see here in America?"

Michael Beckerman, TikTok's head of public policy for the Americas, said the concern is overstated and "makes for good politics." He said TikTok collects less data than other social media apps and is also working to move user data to servers in the U.S. — out of reach of China.

"This would be the firewall," Beckerman said. "Nothing is bulletproof, but for the concerns that are being raised on this, yeah, this is bulletproof."

The Biden administration is investigating TikTok's plan to house its data in the U.S. as part of a sweeping years-long review over whether the company's ties to China are a national security threat. It's unclear when the probe will end.

And more scrutiny is on the way. A top Republican House aide told CBS News that investigating TikTok's links to China will be a priority as the GOP takes control of the House in January.

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