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The FBI on Monday warned U.S. businesses that hackers have used malicious software to launch destructive cyberattacks in the United States, following a crippling hack last week at Sony Pictures Entertainment. The five-page "flash" warning issued to security professionals at U.S. companies provided some technical details about the malware that was used in the attack, though it did not identify the victim by name. The report said that the malware overrides data on hard drives of computers, which can make them inoperable and shut down networks, Reuters reported.

The FBI told NBC News it is "working with our interagency partners to investigate the recently reported cyber intrusion at Sony Pictures Entertainment." U.S. officials are investigating whether North Korea was involved in the attack, which is said to have caused serious damage to the company's databases. The advisory sent out Monday night is not about a new malware attack.



— Reuters and NBC News' Rich Esposito and Pete Williams