Twitter has threatened to sue Meta alleging it stole the company’s trade secrets when creating its rival messaging app Threads, as the new platform attracted tens of millions of users within hours of its debut.

Meta unveiled Threads on Wednesday as a competitor to Elon Musk’s Twitter. Chief executive Mark Zuckerberg said on Thursday that more than 30mn people had signed up less than 24 hours after it had been rolled out, putting it on track to surpass OpenAI’s chatbot ChatGPT as the most rapidly downloaded consumer app at launch.

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” in a letter addressed to Zuckerberg dated Wednesday.