Uber was apparently hacked by a teen, and employees mistook it for a joke.

Uber says it’s investigating a “cybersecurity incident” amidst reports that the company’s internal systems have been breached. The alleged hacker, who claims to be an 18-year old, says they have administrator access to company tools including Amazon Web Services and Google Cloud Platform.

The New York Times reports that the ride-hailing business has taken multiple internal systems, including Slack, offline while it investigates the breach.

The New York Times reports that the ride-hailing business has taken multiple internal systems, including Slack, offline while it investigates the breach.

The hacker appears to have made themselves known to Uber’s employees by posting a message on the company’s internal Slack system. “I announce I am a hacker and Uber has suffered a data breach,” screenshots of the message circulating on Twitter read.

The claimed hacker then listed confidential company information they said they’d accessed, 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, the Washington Post reports.

 Employee responses to the post included lighthearted emoji like sirens and popcorn, as well as the “it’s happening” GIF. One unnamed Uber employee told Yuga Labs security engineer Sam Curry that staff were interacting with the hacker thinking they were playing a joke.

“Sorry to be a stick in the mud, but I think IT would appreciate less memes while they handle the breach,” one employee’s response read, according to The Post.