Threads, Meta’s Twitter rival, is attracting users at an astonishing rate, amassing 10 million signups in just seven hours, according to co-founder and CEO Mark Zuckerberg. But the long-awaited new service, which requires an Instagram Account for onboarding, contains an intriguing stipulation: deleting a Threads account terminates the associated Instagram account.

In a ‘Additional Privacy Policy,” explains Meta, “You can deactivate your Threads profile at any time, but your Threads profile can only be deleted by deleting your Instagram account.”

The rationale, Meta explains on the policy page, is that a Threads profile is part of the user’s Instagram account. The discovery of this provision has surprised many users.

Threads, a text-based conversation app, is the high-profile alternative to Twitter, Elon Musk’s social media platform.

Instagram, the popular photo-sharing platform with more than 2 billion users, rolled out Threads to users in more than 100 countries on Wednesday. The app, the latest in a series of fast-growing Twitter rivals, appears to be the most sought after yet.

Zuckerberg said on Thursday that the app had attracted 10 million signups in just seven hours, sharing an emoji suggesting his mind was blown away by the reception. The pace to 10 million makes Threads the fastest growing consumer offering.

A number of brands including Netflix, Amazon, NFL, Pepsi have also expressed their confidence in Threads by signing up to the app. However, many big names – Google, Apple, Goldman Sachs, Morgan Stanley and Disney – remain mysteriously absent, at least as of the time of publication.