Before I go in-depth I feel it’s important to inform you that only a small portion (93,000 accounts, which is nearly 0.1%) of PlayStation Network, PlayStation Entertainment Network, and Sony Online Entertainment related accounts will be / have been affected.
Apparently data was released from “other” sites / source, and not Sony. This data included sign-in IDs and passwords. A “massive set of sign-in IDs and passwords against [the Sony] network database.” Meaning, if your sign-in ID has been linked to the “hacked” sources, and you made your password to match, your account may be affected.
Sony has “locked” all possible accounts threatened by the attack. You will be forced to reset your password (via email) if your account was affected by the attack. It is probably safe to say this will not result in a shut down of Sony services, like the PlayStation Network hack that occurred earlier this year.
As an extra precaution, all users who use the same password across several websites (Sony related or not) are urged to change them to avoid any possible attack. You can read the full article by Sony here.