Uber said on Thursday it is responding to a cybersecurity incident, after the New York Times reported that a hack had breached the company’s network and forced it to take several internal communications and engineering systems offline.

A hacker compromised an employee’s workplace messaging Slack app and then used it to send a message to Uber employees announcing that it had suffered a data breach, the Times reported citing an Uber spokesperson.

It appeared the hacker was able to gain access to other internal company systems, posting an explicit photo on an internal information page for employees, the report added. “We are in touch with law enforcement and will post additional updates here as they become available,” Uber said in a tweet without providing further details.

The Slack system was taken offline on Thursday afternoon by Uber after employees received the message from the hacker, according to the Times report, citing two employees who were not authorized to speak publicly.

“I announce I am a hacker and Uber has suffered a data breach,” the message read, and went on to list several internal databases that were claimed to be compromised, the report added.

Staff at the company was instructed to not use Slack, which is owned by Salesforce Inc, according to the report. Other internal systems, too, were reportedly inaccessible.