It's worth noting that this attack, if true, is not comparable to the 2011 PSN outage. Whereas the incident three years ago was due to compromised systems and an intrusion into Sony servers, a DDoS attack is much simpler, and basically floods the targeted network with data so that it can't make new connections to legitimate users.
Should the issue escalate or resolve, we'll keep you posted.
Update: Sony is aware of the issue and working to resolve connection problems, according to the official PlayStation Twitter account.
Update 2: Sony has posted an update to the PlayStation Blog, clarifying that "no personal information has been accessed."
Update 3: Sony announced Monday morning that PSN is back online, and the maintenance that was due to take place today is being rescheduled.
Sony PlayStation 3 (late 2012)
Sony PlayStation 4