Stack Overflow hacker went undetected for a week

Stack Overflow now says hacker might have also accessed user data.
Written by Catalin Cimpanu, Contributor
Image: iStock/monsitj

The hacker who breached Stack Overflow last week managed to access data on user accounts, the company said today in an update on its investigation into a security breach it disclosed last night.

The update comes to shed some light into what happened on the company's servers last week, after Stack Overflow left many users scratching their heads when it posted a very short message on Thursday, announcing a severe breach of its production systems.

While it initially said that there was no evidence of the hacker accessing user data, the company changed its statement today.

"While our overall user database was not compromised, we have identified privileged web requests that the attacker made that could have returned IP address, names, or emails for a very small number of Stack Exchange users," said Mary Ferguson, VP of Engineering at Stack Overflow.

The exec said the company is now reviewing log files to determine which users were impacted by the hacker's scans. Users found to have had their info viewed or collected by the hacker, will receive a notification, she said.

Hacker was undetected for days

Further, Ferguson also added a correction to the breach's timeline, which started a week before Stack Overflow thought it did.

"The intrusion originated on May 5 when a build deployed to the development tier for stackoverflow.com contained a bug, which allowed an attacker to log in to our development tier as well as escalate their access on the production version of stackoverflow.com," Ferguson said.

"Between May 5 and May 11, the intruder contained their activities to exploration," the Stack Overflow exec said, highlighting the reason why the company did not detect the intrusion.

"On May 11, the intruder made a change to our system to grant themselves a privileged access on production. This change was quickly identified and we revoked their access network-wide, began investigating the intrusion, and began taking steps to remediate the intrusion."

Stack Overflow said it terminated the hacker's access to its network and is now working with a forensics firm to audit its logs and trace the intruder's actions on its servers.

The company said the investigation is still ongoing and more updates will follow.

Updated at 4:35pm ET: In an email received after this article's publication, a Stack Overflow spokesperson told ZDNet that the number of affected users is around 250.

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