The ruling, issued on April 26, became public on Monday when it was served on mobile service providers. It took effect the same day at 2 p.m. local time (1 p.m. ET); as of that time, people in Brazil who tried to use the service could not connect, nor could they send or receive any messages. Failure to comply will subject the service providers to a fine of 500,000 reals per day ($142,000 per day).

WhatsApp is the most-used app in Brazil, a country of 200 million people (it is now owned by Facebook, the country's second-most used app). An estimated 91 percent of Brazilian mobile users nationwide — more than 100 million individuals — use WhatsApp to communicate with one another for free (it has 900 million active daily users around the world). Brazilians spent this morning, in the hours before the block took effect, frantically sending each other messages on WhatsApp warning that the service was going down for three days.