Variety reports that all Sony Pictures Entertainment employees were advised on Monday, November 24, 2014, not to connect to corporate email or corporate networks following a breach by hackers calling themselves "Guardians of Peace," or #GOP.

Deadline.com reports that Sony Pictures' computers were still down worldwide as of the following day, November 25, 2014.

According to The Verge, company computers were defaced with a message stating, "Hacked By #GOP."

"Warning: We've already warned you, and this is just a beginning," the message adds. "We continue till our request be met. We've obtained all your internal data including your secrets and top secrets. If you don't obey us, we'll release data shown below to the world."

Below the message was a list of five links to zip files allegedly containing stolen data.

A Reddit post examining the zip files reports that they contain several files named "private key," along with Excel files named "passwords" and PDF files named "Diaz, Cameron - Passport.pdf" and "Angelina Jolie passport.pdf." Another poster found what appears to be weekly Excel files backups of a 1Password database.

In an email sent to The Verge, a GOP hacker claimed they were assisted by insiders at Sony, stating, "Sony doesn't lock their doors, physically, so we worked with other staff with similar interests to get in," the hacker added.

HyTrust vice president Michele Borovac told eSecurity Planet by email that this appears to be yet another example of a massive insider breach. "While it’s possible that the statements made by the attacker are just bluster, the reality is that privileged user credentials can give a hacker the keys to the kingdom," she said.

"Organizations must take steps to gain control and maintain visibility over these administrative 'super user' accounts if they want to prevent -- or at least contain -- these types of attacks," Borovac added.

A Courion survey recently found that IT managers are overconfident about their ability to prevent insider breaches, while a SpectorSoft survey found that 61 percent of IT professionals say they're unable to deter insider threats. A recent eSecurity Planet article offered advice on how to defend against such threats.

Incapsula security researcher Ofer Gayer told eSecurity Planet that the Sony attack is a hard blow for the company, particularly coming so soon after Sony's networks were taken offline by a DDoS attack in August 2014.

"As we've seen, these attacks can have a devastating effect on a company, its employees and its clients," Gayer said. "Releasing private data (dubbed 'd0xing' in internet slang) or losing it all completely takes a dangerous step forward from plain old data theft, and as these types of attacks gain popularity, CISOs will be under heavier pressure to prevent them."

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