Uber Investigating Breach of Its Computer Systems

Several of the company's internal systems were taken offline as it investigated the extent of the hack.

Two employees who were not authorized to speak publicly said that employees were told not to use the company's internal messaging service, slack, and that other internal systems were not accessible.

A spokesman for the company said it was looking into the incident.

Shortly before the Slack system was taken offline on Thursday afternoon, employees of the company received a message saying that they had been a victim of a data hack. Several internal databases were listed by the hacker as having been compromised.

The hacker used a worker's account to send a message. The hacker gained access to other internal systems after posting an explicit photo on an internal information page for employees.

A hacker has stolen data before. In 2016 hackers stole information from 57 million driver and rider accounts, then asked for $100,000 to destroy their data. The payment was arranged but the breach was not made public.

Sullivan was fired for his role in the response to the hack. Mr. Sullivan is on trial for obstruction of justice for failing to tell regulators about the problem.

Sullivan have argued that other employees were to blame for regulatory disclosures.