According to Engadget, the offending PSN message contains an unrecognised character which "effectively bricks their consoles". Where the PS Messages app/database rebuild option preserves all the data on your console's hard drive, a factory reset wipes everything.
For starters, users can lock down their PSN message permissions to only allow messages from friends. The instructions also advise deleting the message from the PlayStation app without opening it, another strategy that some players had already employed. Reports indicate that some PS4 consoles continue to operate unstably even after the message is deleted; in that instance a rebuild of the PS4 system database has been reported to fix any lingering issues.
Reddit user ThatPissedOffDude said: "This just happened to me during Rocket League". We all have had to factory reset. Others have reported similar problems after receiving a message with unrecognized characters. "Only one of our guys wasn't affected and he has his messages private".
As of right now, there is no comment from Sony regarding the PS4 messaging hack. You can do that by going to Account Management in your console Settings, heading to the Privacy Settings submenu, and changing Messaging settings to "Friends Only" or "No One", meaning that only your pre-selected friends or no one at all can message you.
In a statement to VG247, Sony revealed that it is "aware of the situation" and the company is in the midst of planning a system update to fix it.