US Congress members have grilled TikTok boss Shou Zi Chew over the the safety of the social media app.

The US has threatened to ban it completely if the company remains under Chinese ownership.

Many Western countries are also taking measures against other Chinese tech firms over security fears.

TikTok is a platform for creating and sharing short videos and is owned by the Chinese company ByteDance.

It was started in 2016, and has become the third most popular internet service in the world, with more than a billion active monthly users.

The app has been banned on government devices in Canada, Belgium, Denmark, New Zealand, Taiwan, the UK and the US.

The EU told its staff to remove the app from phones it has issued, and also recommended they remove it from private devices on which official apps are installed.

India has banned TikTok outright because of security concerns.

Afghanistan has also banned it to prevent young people from "being misled".

TikTok gathers the same type of user data as many other social media firms such as Facebook and Instagram.

This includes names, ages, phone numbers, email addresses and photos.

FBI director Chris Wray has pointed to China's 2017 National Intelligence Law, saying it requires companies "to do whatever the government wants them to do in terms of showing them information or serving as a tool for the Chinese government."

TikTok also has a tool which recommends video clips for users to watch, called the "For You" feed, which experts say is better designed than those used by Facebook or Youtube.

"TikTok has a more complex model in terms of showing content to its users," says Dr Maryam Mehrnezhad from the Department of Information Security at Royal Holloway, University of London. "This makes the spread of misinformation easier and its identification and detection more difficult."

Chinese companies specialising in 5G technology such as Huawei, ZTE and Hytera have been banned from installing equipment on networks in Australia, the US, Japan, India, and Canada.

The UK government has ordered equipment installed by Huawei to be removed from 5G networks by 2027.

The US and Dutch governments are restricting the export of semiconductors to China because of security fears over the country's development of supercomputing and AI technology.

The UK and Australian government have ordered Chinese-made security cameras to be removed from sensitive sites.

Governments fear that 5G equipment installed by Chinese firms in foreign countries' networks contains "backdoors" through which data can be passed back to Beijing.

Through companies such as Hikvision, China is the world's largest producer of security cameras. It is thought that that these could also be secretly feeding intelligence to China.

"Why wouldn't they have put in backdoor access?" asks Prof Anderson. "Western countries have done that for years when they've built telephone networks around the world."

There's no hard evidence that China is using its tech firms for espionage, says Jake Moore, global security advisor to ESET, an internet security firm.

However, he says: "There's a fear that firms like Huawei and TikTok have become so big that they could be hacking huge amounts of data and damaging national security.

"Governments are right to take precautions against it now rather than later."

China's foreign ministry has called the bans on TikTok and other tech firms "political theatre", saying the "US is overstretching national security concerns to suppress other countries' companies."

TikTok insists it gathers no more data than other social media apps, and is independent of the government.

In 2022, it admitted that some of its staff in China could access user data gathered in Europe, but it says that it is working on ways of keeping such information within Europe.

It also says that American users' data is nowadays processed through US servers, and does not go to China.

(editor-in-charge：Press center4)