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User Data Exposed in Stack Overflow Hack

Hackers had access to Stack Overflow systems for nearly one week before the attack was detected and some user data was exposed after all, the company has admitted.

Stack Overflow informed users on May 16 that it had detected unauthorized access to production systems over the previous weekend. The company initially said it had found no evidence that customer or user data was compromised.

In an update posted on May 17, Stack Overflow VP of Engineering Mary Ferguson revealed that the initial intrusion apparently occurred on May 5. The attackers managed to access the development tier for stackoverflow.com due to the fact that a build deployed on that day contained a bug. The hackers then escalated their access to the production version of the website.

Stack Overflow hacked

The attackers mainly focused on reconnaissance until May 11, when they made a change that gave them privileged access to production systems.

“This change was quickly identified and we revoked their access network-wide, began investigating the intrusion, and began taking steps to remediate the intrusion,” Ferguson explained.

Ferguson says the company has separate infrastructure and networks for its Teams, Business and Enterprise products and there is no evidence that any of these systems or their customers have been impacted. Stack Overflow’s Advertising and Talent units also don’t appear to be affected.

However, the investigation has revealed that the attackers made some privileged requests that could have allowed them to obtain the names, email addresses and IP addresses of some Stack Exchange users.

The company claims roughly 250 public network users appear to be impacted and they are being notified.

Stack Overflow has contracted a third-party forensics and incident response firm to assist its investigation, and says it’s resetting passwords and taking other “precautionary measures” in response to the incident.

With 10 million registered users and over 50 million unique visitors every month, Stack Overflow is the main website of the Stack Exchange Network.

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Eduard Kovacs (@EduardKovacs) is a contributing editor at SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.