FireEye stock tumbles 13% after the cybersecurity group reveals hackers breached its defenses and stole diagnostic tools

• FireEye stock slumped as much as 13% on Wednesday, wiping $450 million off the cybersecurity group's market capitalization.
• The company revealed on Tuesday that hackers recently breached its defenses and stole tools it uses to test customers' protections.
• "We were attacked by a highly sophisticated threat actor, one whose discipline, operational security, and techniques lead us to believe it was a state-sponsored attack," FireEye CEO Kevin Mandia said in a blog post.
• FireEye is working with the FBI, Microsoft, and other partners to investigate the theft, and has developed and shared more than 300 countermeasures to the stolen diagnostic tools.
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FireEye shares tumbled as much as 13% on Wednesday, slashing the cybersecurity group's market capitalization by up to $450 million. The selloff was sparked by FireEye's disclosure that ostensibly state-sponsored hackers recently broke through its defenses and stole security-testing tools.

"We were attacked by a highly sophisticated threat actor, one whose discipline, operational security, and techniques lead us to believe it was a state-sponsored attack," FireEye CEO Kevin Mandia said in a blog post on Tuesday after the market close.

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The hackers appeared to be "highly trained," displayed "top-tier offensive capabilities," and employed a "novel combination of techniques" to break through FireEye's digital fortifications and access its Red Team tools, which mimic cyber attacks to pinpoint weaknesses in its customers' protections.

FireEye has roped in the FBI and partners such as Microsoft to help it investigate the incident, Mandia said. It has also developed and shared more than 300 countermeasures in case the thieves deploy its diagnostic tools in the coming weeks.

The stock-price drop likely reflects concerns that FireEye's customers will be less trusting of the company's ability to ward off attacks if its own systems can be breached. Investors may also be worried that FireEye's tools could be blamed for future cyberattacks, or the company could fall victim to further attacks.

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The cybersecurity group's profile has grown in recent years, as it has helped companies such as Sony and Equifax deal with high-profile attacks. It was also called in when Russian hackers broke into US government systems in 2015.