“Certainly the government’s overarching national-security interest is significant,” Beeler’s ruling said. “But on this record – while the government has established that China’s activities raise significant national security concerns – it has put in scant little evidence that its effective ban of WeChat for all US users addresses those concerns.”

The Commerce Department said on Monday it will challenge the court’s order, saying that the prohibition of identified transactions on WeChat is necessary to protect US national security, according to a Reuters report.

Here is what you need to know about what these developments mean and what could happen next.

Why is WeChat so important to the people who use it?

WeChat, or Weixin as it is known in mainland China, began life at internet giant Tencent Holdings’ Guangzhou Research and Project centre in October 2010. Since then, it has grown into the most popular mobile app in the country with more than 1.2 billion monthly active users who chat, play games, shop, read news, pay for meals, and post their thoughts and pictures. With the app, people can even book a doctor’s appointment or arrange a time slot to file for a divorce at the civil affairs authority.

The multipurpose app has also laid the foundations for stellar growth at Shenzhen-based Tencent, turning it into one of the most influential companies in China and grabbing the attention of global investors. Since the official launch of WeChat in January 2011, Tencent’s market capitalisation has risen over tenfold.

In the US, most of WeChat’s users are part of the Chinese diaspora. The app has an average of 19 million daily active users in the US, according to analytics firm Apptopia.

Trump targeted both WeChat and TikTok with US bans – why then did it seem Tencent was getting an easier ride?

While there are many popular social messaging apps in the West like Facebook Messenger, WhatsApp, Line and Telegram, these are all blocked by China’s Great Firewall.

With the increased tensions between Beijing and Washington, WeChat – along with popular ByteDance-owned short video-sharing app TikTok – recently became the latest targets of the Trump administration’s scrutiny. An executive order issued by US President Donald Trump on August 6 seeks to prohibit any transaction between WeChat and US individuals and companies, citing the app’s data collection method as a threat that would “allow the Chinese Communist Party access to Americans’ personal and proprietary information”. That ban was to take into effect on September 20, but was halted by the California court’s ruling.

WeChat “serves as a virtual public square for the Chinese-speaking and Chinese-American community in the United States and is (as a practical matter) their only means of communication”, Magistrate Judge Laurel Beeler wrote in her decision. She said that banning the app “forecloses meaningful access to communication in their community and thereby operates as a prior restraint on their right to free speech”.

Given the constitutional questions brought up by the lawsuit filed in August against the executive order by the US WeChat Users Alliance, analysts said the judge made a reasonable call.

“Given the politically charged atmosphere and the nexus with national security, this ruling is … most welcome for the plaintiffs,” said Nathaniel Rushforth, a lawyer and cybersecurity specialist at Shanghai-based DaWo Law Firm. “It demonstrates that the judge is, at least, somewhat sympathetic to some of the plaintiffs’ arguments.”

So can WeChat now be used in the US without any problems after the court ruling?

With the preliminary injunction in place, the answer is yes.

Apple’s App Store and Google Play as well as US mobile network service providers can all continue to support the various functions of WeChat. As such, people in the US can use the app as usual, according to a statement by the US WeChat Users Alliance. “The injunction will remain effective … unless the government appeals and the injunction is reversed,” a representative of the alliance said on Sunday.

“There are probably other ways the administration could act to ban WeChat, but they are likely to be met with as much legal resistance as we are currently seeing,” said Rushforth of DaWo Law Firm. “The government can, and likely will file an appeal. Whether they win that appeal depends on a number of things, including some procedural complications, so it will be an uphill battle.”

Other law practitioners, however, indicated that the California court’s ruling was merely “a stay of execution”.

“It’s only an injunction and there will be further and more involved hearings to determine whether the WeChat ban is indeed unconstitutional,” said Paul Haswell, a partner who advises technology companies at international law firm Pinsent Masons. “A lot can happen in US politics between now and then.”

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What happens if the Trump administration goes ahead?

That would effectively ban American app stores from offering WeChat. Users in the US will not be able to find the app for download on Apple’s App Store or Google Play.

For US users who already have WeChat installed on their smartphones, they could possibly still use the app on their existing devices. But if they buy a new smartphone, they will not be able to reinstall the app.

Under the US government’s ban, the country’s internet services providers and mobile network operators will not be allowed to work with WeChat. If servers in the US stop sending WeChat data between users within the country as well as between users in the US and China, the app would become extremely slow as to render it virtually unusable.

US users also would not be able to download any software updates for WeChat. App makers update their apps from time to time to add new functions or patch security holes. Those updates in the US are generally dispatched via Apple and Google’s app stores.

Are there alternative apps that US users can switch to?

Yes, there are other messaging apps that work both in China and the US.

WeChat Work, now rebranded as WeCom, is designed for work collaboration. But it can be linked to a WeChat account to message or receive money from WeChat friends.

QQ is another social messaging app from WeChat operator Tencent. It may not be as popular as WeChat, but it is still used by millions of people in China. It can be downloaded from app stores on both sides of the Pacific. Also, QQ’s electronic wallet function is compatible with that of WeChat’s.

Signal, a cross-platform encrypted messaging service, is a better option if US users are concerned about privacy. Unlike WeChat or QQ, Signal’s end-to-end encryption means any message that is intercepted during transmission cannot be deciphered. Only the intended recipient has the key to decrypt such a message. Despite being an American app, Signal currently works in China.

Otherwise, for both iOS and Android users, videoconferencing apps like Zoom and Skype are available in China and the US. So are office apps like DingTalk from Alibaba Group Holding, parent company of the South China Morning Post.

Beijing condemns Trump ban as WeChat’s US users brace for a life of ‘inconvenience’

What if US users still insist on having WeChat after Trump’s ban proceeds?

Users can try, but there is no guarantee that the app will work without any hitch.

One suggested method is to manually install WeChat onto a smartphone from a computer file, a process known as “sideloading”. Android device users can look for these files online with search terms like “WeChat APK”.

The situation will be much harder for iPhone users. That involves a process called “jailbreaking”, which can be searched online.

Sideloading or jailbreaking are not without risks. When you download an app from Google or Apple’s store, you know that it has been vetted for bugs or privacy issues. Downloading the same app from other places does not give you the same peace of mind.

Probably the safer way is to download WeChat from Google and Apple’s foreign app stores. On an iPhone, you can switch to a non-US App Store by changing the country or region that your Apple ID is associated with. Google Play accounts work similarly. This way you can also continue to receive the latest app updates for WeChat.

Once you have the latest version of WeChat, you can use a virtual private network (VPN) to connect to a server outside the US and access WeChat as usual. But this will only work if Tencent does not actively block American users. If the company ever decided to stop anyone with a US SIM card from using WeChat, then US users will have to take out the SIM card and use a VPN.

A final word of caution: whenever you install a new WeChat app on your smartphone, your contacts and electronic money will stay in the same account – but not your messages. That is why before you delete your old app or switch to a new smartphone, remember to back up your messages. You can easily do that by logging into WeChat Desktop on PC or Mac.