On April 20, 2011, Sony shut down the PlayStation Network and Qriocity for a prolonged interval, revealing on April 23 that this was due to "an external intrusion on our system". Sony later revealed that the personal information of 77 million users might have been taken, including: names; addresses; countries; email addresses; birthdates; PSN/Qriocity logins, passwords and handles/PSN online IDs. They also stated that it was possible that users' profile data, including purchase history and billing address, and PlayStation Network/Qriocity password security answers may have been obtained. There was no evidence that any credit card data had been taken, but the possibility could not be ruled out, and Sony advised customers that their credit card data may have been obtained. Additionally, the credit card numbers were encrypted and Sony never collected the three digit CVC or CSC number from the back of the credit cards which is required for authenticating some transactions. In response to the incident, Sony announced a "Welcome Back" program, 30 days free membership of PlayStation Plus for all PSN members, two free downloadable PS3 games, and a free one-year enrollment in an identity theft protection program.
Try to answer this question if possible (otherwise reply "unanswerable"): What was the date Sony shut down the PS Network because of a security breach?
April 20, 2011