A statement issued by Sony Online Entertainment explains that users who have been affected by the recent server downtime will get 30 days subscription free, and one extra day for every day they've been affected.
They also revealed that every player who has suffered will receive a free in-game item that will be a Batman-inspired mask, but it will only affect appearance.
Sony Online Entertainment had to take down their servers decently due to a similar security intrusion suffered by the PlayStation Network. There's no word when their servers will be back up.
Source: Official Facebook Page