The office will be headed by Twitter executive Peter Greenberger.

Xiaomi Inc said it had upgraded its operating system to ensure users knew it was collecting data from their address books after a report by a computer security firm said the Chinese budgetsmartphone maker was taking personal data without permission.

Before it backtracked, Twitter had said Thursday that the change was meant to protect victims of harassment who wanted to filter out abusive messages but feared that the act of blocking a user would prompt retaliation.