San Francisco,  An 18-year-old hacker has broken into the internal systems of Uber, reaching company tools including Amazon Web Services and Google Cloud Platform, and employees thought someone was playing a prank.

The hacker made himself known to Uber employees by posting a message on the company's internal communication system Slack.

"I announce I am a hacker and Uber has suffered a data breach," screenshots of the message circulating on Twitter read.

The hacker then listed confidential company information and posted a hashtag saying that Uber "underpays its drivers".

The Slack message from the alleged hacker "was so brazen that many Uber employees appear to have initially thought it was a joke", reports The Washington Post.

Some employees even responded to the hacker with emoji like sirens and popcorn, as well as the "it's happening" GIF.

One unnamed Uber employee told bug bounty hunter and security engineer Sam Curry that staff were interacting with the hacker thinking "they were playing a joke".

Uber said in a statement that it was investigating a "cybersecurity incident" while it took Slack offline for employees.

"We are currently responding to a cybersecurity incident. We are in touch with law enforcement and will post additional updates here as they become available," Uber posted in a tweet.

An Uber employee posted that they were told to stop using Slack as "anytime I request a website, I am taken to a page with a pornographic image" and the message "f*** you wankers".

The hacker reportedly said he broke into the Uber systems because "they had weak security".