Threads, described as a “text-based conversation app”, is linked to Meta-owned Instagram and went live at midnight on Thursday.
As numbers continued to grow, a threat of legal action emerged from Twitter, alleging that Meta stole trade secrets - something that appeared to be denied by the Instagram and Facebook owner.
READ MORE: Expert analysis and opinion from Yahoo UK's partners on Threads
Mark Zuckerberg trolls Elon Musk by posting Spider-Man meme on Twitter after launching rival Threads (Independent, 2-min read)
The launch of Meta’s Threads proves yet again we are too much in awe of the internet (Guardian, 4-min read)
How to delete your Threads account (Techradar, 3-min read)
Will Threads kill Twitter? (The Week, 4-min read)
Alex Spiro, a lawyer for Twitter, accused Meta of engaging in “systemic, wilful, and unlawful misappropriation of Twitter’s trade secrets and other intellectual property”.
The letter, which was first reported by Semafor, accused Meta of hiring “dozens” of former Twitter employees who “have access to Twitter’s trade secrets and other highly confidential information”.
In a tweet referencing the letter on Thursday evening, Twitter owner Elon Musk said: “Competition is fine, cheating is not.”
On Threads, Meta communications director Andy Stone posted in relation to the report: “No one on the Threads engineering team is a former Twitter employee — that’s just not a thing.”
US copyright law does not cover ideas so Twitter will need to prove that intellectual property has been stolen if the dispute is taken to court.
Posting his hopes on app user numbers as the platform launched, Zuckerberg said: “I think there should be a public conversations app with 1 billion+ people on it. Twitter has had the opportunity to do this but hasn’t nailed it. Hopefully we will.”
High-profile Threads users already including chef Gordon Ramsay, pop star Shakira and Mark Hoyle, better known as the YouTuber LadBaby.
The huge numbers joining the app may be down to frustrations over changes to Twitter introduced after Elon Musk's takeover in October.
In the latest of a spree of technical problems faced by the micro-blogging site, Musk announced last week that Twitter was temporarily limiting the number of tweets people could read each day.
Many users are unhappy that having a "verified" account has become monetised, a move which initially saw a slew of impersonator accounts spreading chaos on the site.
To top that off, Twitter has crashed multiple times since Musk stepped in, with many suggesting it could be related to 80% of the site's 8,000 global staff being fired since the takeover.
Whatever the source of users' frustration, social media consultant and industry analyst Matt Navarra says they are "desperately looking for an exit from the platform".
Here, Yahoo News explains how Meta's Threads app works and the potential threat it poses to Twitter's supremacy.
What is Threads?
Threads is a "text-based conversation app", where "communities come together to discuss everything from the topics you care about today to what’ll be trending tomorrow", according to a description on the App Store.
Shots of the app show a similar format to Twitter, with the flexibility to share posts with absolutely anyone on the site, only people you follow (similar to Twitter Circle), or only users you've mentioned.
One of the biggest draws for users could be the fact that accounts are linked to people's Instagram profiles, meaning it's easier to start off with a network of friends and followers.
“Users of Twitter are desperately looking for an exit from the platform to escape, and the existing options of rivals are fairly limited," says Navarra.
Since Musk's takeover alternative platforms such as BlueSky, Mastodon and Tribel have enjoyed increased exposure, but users have complained of functionality issues with many Twitter rivals.
Navarra adds: “They all have the same big problem, which is you have to start from zero – it’s a network that is completely new.
"One of the biggest benefits for Meta is that it’s building off the back of Instagram, where people are familiar and can also kickstart their following because it ties into the same social graph.”
Furthermore, Meta is a $732.99bn company, meaning it may be a big enough behemoth to pose a serious challenge to Musk.
How is it different to Twitter?
One of the main differences between Twitter and Threads is that the newcomer is decentralised.
This means that the network comprises of many interconnected servers running independently of each other, rather than being connected to one huge central server.
This follows a similar model to cryptocurrency, and to Twitter competitor Mastodon.
In fact, Threads will use the same ActivityPub social media protocol as Mastodon, meaning that in theory users of either platform could interact, although this remains to be seen.
One of the main benefits of decentralised social networks is that they give users more control over their personal data, more control over user-made content, and better protection against censorship.
What data does Threads collect?
Adopting a decentralised model may be a good PR move, but Facebook's involvement in the Cambridge Analytica scandal will still be fresh in many people's minds.
Late last year Meta agreed to pay $725m to settle a long-running lawsuit that claimed Facebook illegally shared user data with the research firm Cambridge Analytica.
Zuckerberg may be hoping to shake this association, but concerns have already been raised about the breadth of data Threads may collect.
A listing on the App Store says data on health and fitness, purchases, financial information, location, contact information, contacts, browsing data, "sensitive information" and more may be collected by the app.
Twitter also collects a lot of data from its users, they are after all, both free by default. Listings for both apps on the App Store suggest Threads collects a wider range of data, but how it will be used is hard to tell.
Meta's chief product officer Chris Cox has previously insisted that the company is providing a "sanely run" platform for which people are crying out.
However, in response to a tweet criticising the jibe, Musk replied: "Thank goodness they're so sanely run."
Navarra adds that while the appetite for change exists among users, it would be weighed up against mixed public opinions on Meta.
The company was fined €1.2bn euros (£1 bn) in May over the transfer of data from European users to US servers.
“Meta and Instagram comes with baggage, a bad name and bad press. People are very wary and sceptical of anything Mark Zuckerberg does,” Navarra says.
He adds that a retaliation from Musk to the Threads launch was very possible given his “tendency to be quite petulant and petty”.
Watch: Could Elon Musk and Mark Zuckerberg fight in Rome's Colosseum?