The only fix for the time being is to prevent yourself from receiving such messages. Head up to the XMB on the PS4, go into Settings, then Account Management. From there, head to Privacy Settings, where you’ll be prompted to input your password. Next, head to Personal Info, followed by Messaging. If you trust all of your friends, feel free to set the privacy setting to Friends, so only they can message you. If your list is full of randos, you might want to consider setting it to “No One” until Sony announces a fix.