Through their official blog, Sony revealed that some hackers managed to access the Playstation Store through PCs and might have changed some users' passwords.
"Although unlikely, it is possible that the passwords of a small percentage of PLAYSTATION Network users may have been changed through unauthorized access, making it possible to view users' personal information and/or use the Wallet for the PLAYSTATION Store", reads the official statement. "PLAYSTATION Network accounts do not display entire credit card numbers, so any unauthorized access to your PLAYSTATION Network account is very unlikely to compromise your credit card number."
Sony noted that they have investigated and rectified the issue and that system security has been restored. Sony will be contacting the users who might have been affected, but in the meanwhile you can check if you have been affected by trying to log in to your Playstation Store account. If you can successfully sign in with your pre-set password, your account is not affected by this incident.