PlayStation Plus subscribers will get five additional days at no extra charge.
Over the weekend, PlayStation Network users were disappointed to find that the service was down for the count. The outage lasted nearly an entire day, effecting not just online play, but virtually every aspect of PlayStation Network connectivity, including the ability to validate certificates and permissions for offline, single-player games. This inconvenience has led Sony to offer PlayStation Plus subcribers five additional days of service at no extra charge.
As for the lingering question of why this outage happened, Sony hasn't revealed anything beyond dubbing the mishap as an "operational issue." Here's the statement made by Sony via X:
The last time PSN had an outage of this magnitude was back in 2011 when the service was hacked. Although Sony hasn't said there was any malicious activity that resulted. in this disruption, if we learn more we'll be sure to share it with you all.
Source: Ask PlayStation X Account