Electronic Arts, a video-game maker, is the latest company to be hacked.

Electronic Arts, the maker of popular video games including the FIFA, Madden, Sims and Medal of Honor series, said Thursday that it was investigating an intrusion into its network that resulted in game source code and tools being stolen.

“We’ve already made security improvements and do not expect an impact on our games or our business,” an E.A. spokeswoman said, adding that the company was working with law enforcement officials to investigate. The company said no player data was affected.

The hacker or hackers claimed to have stolen important source code for the 2021 edition of the popular soccer game FIFA, as well as data related to a gaming creation engine called Frostbite, according to online posts made in early June on an underground forum frequented by cybercriminals. E.A. confirmed that portions of FIFA and Frostbite code had been stolen.

The posts were reviewed by Intel 471, a cybercrime intelligence firm, which said the hackers were advertising about 800 gigabytes worth of data. The incident was first reported Thursday by Vice News.

Michael DeBolt, Intel 471’s senior vice president of intelligence, said a hacker was advertising stolen E.A. data on a Russian-language forum as long ago as early May. That hacker offered the stolen information for a starting bid of $500,000, Mr. DeBolt said, but it was unclear whether a sale had been made or if there was a connection between the various people advertising the data.

Now, he said, a squabble has broken out on the online forums over which thief can lay claim to the crime and deserves to make money off the stolen material. “All other offers are scam or fake,” one user wrote, according to a screenshot.

“Surprisingly, cybercriminals can’t work nicely together and say nice things about each other,” Mr. DeBolt said.

He said that at least one of the people had offered some evidence through screenshots of access to stolen E.A. files. “It lends to the assessment that this claim could be credible and it needs to be investigated fully,” he said.

E.A. is the latest in a series of companies to be hit with cyberattacks in recent months, including the world’s largest meat processor, JBS, and the Colonial Pipeline, which provides fuel along the East Coast. Those hacks were ransomware attacks, where hackers attempt to shut down systems until a ransom is paid, but E.A. said it had not received any ransom requests.