Sony has announced that online matchmaking for the PlayStation Network is back online, and that a mandatory install of a new firmware will be required.
According to the blog post, update 3.61 is mandatory and as soon as you log into PSN, here is what you need to do:
If using a PS3, your password can only be changed on your own PS3 (or a PS3 on which your PSN account was activated), as an added layer of security. If you have never downloaded any content using your account on the system, an email will be sent to the registered sign-in ID (email address) associated with your account when you first attempt to sign-in to PSN. This e-mail will contain a link that will enable you to change your password. In this email, click on the link and follow the instructions to change your password. Once you have changed your password you can sign-in to your account using your new password.
We strongly recommend that all PSN account holders with PS3s update their systems to prepare for when PlayStation Network is back online. The release of this update is a critical step as we work to make PlayStation Network significantly more secure. Thank you for your continued support and patience.