Montana has become the first US state to ban TikTok on all devices, even personal ones, triggering renewed doubts about the short-form video app's future in the country.

On Wednesday, the state's governor, Greg Gianforte, signed a bill into law that would fine TikTok and online app stores for making the service available to state residents. It takes effect next year.

The move goes a step beyond other states that have restricted TikTok from government devices. It also comes at a time when some federal lawmakers are pushing for a nationwide ban.

But legal and technology experts say there are huge hurdles for Montana, or any state, to enforce such a law. The TikTok ban immediately prompted one lawsuit from TikTok users who allege it violates their First Amendment rights, with more legal challenges expected. Even if the law is allowed to stand, the practicalities of the internet may make it impossible to keep TikTok out of the hands of users.

How can a state ban TikTok?

Montana's new law, SB419, makes it illegal for TikTok and app marketplaces to offer the TikTok service within state lines.

Passed in April, the bill establishes fines of $10,000 per violation per day, where a single violation is defined as "each time that a user accesses TikTok, is offered the ability to access TikTok, or is offered the ability to download TikTok."

Individual users themselves would not be on the hook just for accessing TikTok, according to the law.

If the law survives in the courts, TikTok, and companies such as Apple and Google, could be forced to find ways to restrict TikTok from Montana smartphone users — or face huge penalties.

But that's a big if.

Will there be legal challenges?

TikTok and other civil society groups warn that the law as written is unconstitutional. There are two main arguments TikTok's defenders have cited.

One is that the law violates the First Amendment rights of Montanans, by restricting their ability to access legal speech and by infringing on their own rights to free expression through the app.

On Thursday, the American Civil Liberties Union accused Gianforte and the state legislature of having "trampled on the free speech of hundreds of thousands of Montanans who use the app to express themselves, gather information, and run their small business in the name of anti-Chinese sentiment."

A group of TikTok users echoed that complaint in a lawsuit filed Wednesday evening in the US District Court for the District of Montana, hours after the governor's signature. "Montana can no more ban its residents from viewing or posting to TikTok than it could ban the Wall Street Journal because of who owns it or the ideas it publishes," according to the complaint.

Another allegation is that the law represents an unconstitutional "bill of attainder," or a law that penalizes somebody absent due process.

NetChoice, an industry trade group that counts TikTok as a member, said the bill "ignores the U.S. Constitution."

"The government may not block our ability to access constitutionally protected speech -- whether it is in a newspaper, on a website or via an app," said Carl Szabo, NetChoice's general counsel.

A spokesperson for Gianforte didn't immediately respond to a request for comment.

How can Montana enforce a TikTok ban?

Even if the law survives a legal challenge, experts say its vagueness could make it difficult to effectively implement and enforce.

"What this really does is create a huge potential liability for both TikTok and the mobile app stores," said Nicholas Garcia, policy counsel at the consumer advocacy group Public Knowledge. "And what it requires them to do is to figure it out, under threat of Montana coming in and saying, 'You have not been complying with the law.'"

It's unclear how, exactly, Montana officials might determine noncompliance.

Authorities could try to subpoena TikTok or the app stores for information on users who have accessed or downloaded TikTok from within the state, but those requests wouldn't capture the many people who would likely circumvent the ban.

Virtual private networking (VPN) services would make it trivial for users to get around the restrictions, according to Evan Greer, director of Fight for the Future, a consumer advocacy group. A VPN could make a user in Montana appear as if they are connected to the internet from outside state lines.

"Any teenage anime fan or British TV aficionado can tell you how to circumvent such a silly ban using a VPN," said Greer.

Officials could potentially try to expand their dragnet by asking companies to use additional data they possess on their users to make inferences about who may be accessing TikTok. But depending on the scope of such a request, it could trigger legal objections and privacy concerns — if the additional data is even available.

Asking internet providers to implement statewide network filters might be another way to enforce the law, said Garcia. But internet providers are not named as a type of entity subject to the TikTok ban.

"So the only reason they would get involved would be if TikTok or Apple and Google wanted them to," Garcia said, "and made some business case for why they should go through that effort on a contractual basis or something."

Why did Montana ban TikTok?

As with the dozens of other states that have imposed some level of TikTok restrictions, Montana's government has cited the app as a potential privacy and security risk.

US officials worry that TikTok's links to China through its parent company, ByteDance, might result in American's personal information leaking to the Chinese government. That could help China with spying or disinformation campaigns against the United States, according to authorities.

So far, though, the risk appears to be hypothetical: There is no public evidence to suggest that the Chinese government has actually accessed TikTok's US user data. And TikTok isn't the only company that collects large amounts of data, or that might be an attractive target for Chinese espionage.

TikTok has said it is executing on a plan to store US user data on cloud servers owned by the US tech giant Oracle, and that when the initiative is complete, access to the data will be overseen by US employees.

More than half of US states have announced some restrictions on TikTok affecting the app on government devices. Montana's ban marks the beginning of a new phase, however — and the widely expected legal challenges may determine whether other states soon follow suit.