The intended use was for a user to submit their contact data (phone book). Twitter's API would return a list of usernames matching those numbers for the purpos

The intended use was for a user to submit their contact data (phone book). Twitter's API would return a list of usernames matching those numbers for the purpose of requesting/notifying/suggesting potential friends (in exchange for their* data used to build a social graph/sell). Twitter patched/updated the API which means (the API probably returns a token or key or something that doesn't reveal the username now) if someone wants to submit a list of phone numbers to get their Twitter usernames they'll have to pay Twitter[0] or use a different "exploit". * if someone has my phone number in their phonebook and gives it to Twitter - it becomes our data. [0] https://business.twitter.com/en/help/overview/what-are-promoted-accounts.html https://business.twitter.com/en/help/overview/what-are-promo...