According to Vice, hackers on various forums claim to have stolen game source code and related internal tools from EA. Some of these forums are locked from public view, but one of Vice's sources has shared screenshots of the messages from the hackers. EA FC 25 Coins itself confirmed the data breach in a statement to Vice. It assures that no player data was accessed, so there shouldn't be any risk to player privacy.
As for what exactly was stolen, the hackers say they have obtained the source code for FIFA 25. as well as code for its matchmaking server. They also claim to have the source code and tools for EA's Frostbite engine. The engine was designed by Battlefield studio DICE and has been used for a wide variety of EA's title, including the Battlefield series, FIFA, Madden, Need for Speed, and a few Star Wars games.
Combined with other stolen information, such as software development kits, the hackers say they have 780GB of data which they intend to sell. They haven't publicly distributed any of the data itself and have only posted screenshots to back up their claims of accessing EA's data. EA is already working with law enforcement and has improved its security in the wake of the breach. It adds that it doesn't expect the incident to have any sort of impact on its games or businesses.
EA is only the latest games company to suffer a hacking incident like this. Earlier this year, Cyberpunk 2077 and The Witcher studio CD Projekt also saw the source code for some of its games be stolen. Unlike EA's hackers, the CD Projekt hacker was willing to return what they stole back to the company if it met their demands, threatening to sell or leak the data if CD Projekt refused, which it did.
And before that, Capcom suffered a possibly even worse data breach. Not only were a swathe of unannounced projects leaked online, but Capcom confirmed that personal data had been obtained as well. Among the victims were customers, employees, and even former employees who weren't with FC Coins for sale the company anymore.