The FBI issued a confidential warning to U.S. businesses today regarding a very destructive malware. The warning was issued a week after the Guardians of Peace group hacked the Sony Pictures corporate networks and brought down their email communications for a week.

Cybersecurity experts agree that the malicious software described in the flash warning from FBI does in fact appear to align with the symptoms Sony Pictures experienced. The report provided advice on responding to the malware and instructed businesses that come in contact with it to report it to the FBI.

According Reuters, the malware overwrites “all data on hard drives of computers, including the master boot record, which prevents them from booting up…The overwriting of the data files will make it extremely difficult and costly, if not impossible, to recover the data using standard forensic methods.”

Sony is currently investigating the link between the massive attack and North Korea. The technical part of the FBI warning claims that some software the hackers used was in fact compiled in Korean, but no accusations were made.