The blockade, which went into effect at midnight, was ordered for 48 hours by a judge in SÃ£o Paulo after Facebook defied orders to turn over data in a criminal court proceeding there. Details of the case were sealed.
But the shut down was quickly overturned on Friday morning by an appeals court. It ruled that it was âunreasonableâ to suspend a service used by millions of people because the company had failed to provide information to the courts.
WhatsApp has about 100 million users in Brazil and is a fixture on most smartphones. The app allows users to send text messages and make voice calls for free, making it an attractive alternative to Brazilâs pricey cellular services.
Facebookâs co-founder and chief executive, Mark Zuckerberg, said it was a âsad dayâ for Brazil.
âUntil today, Brazil has been an ally in creating an open Internet,â he wrote in a Facebook post in English and Portuguese. âI am stunned that our efforts to protect peopleâs data would result in such an extreme decision by a single judge to punish every person in Brazil who uses WhatsApp.â
Foreign governments have become increasingly willing to block American Internet services as part of legal disputes. Turkey, for example, has cut off Twitter and YouTube, which is owned by Google, in the past for failing to take down content that the government found objectionable.
Mr. Zuckerberg urged Brazilians to press their government to overturn the ban. He also encouraged them to use Facebookâs other instant-messaging service, Messenger, as an alternative.