Twitter allows users to candidly interact with people all around the world. But its open nature also exposes many to harassment and abuse from users. Twitter CEO Dick Costolo recently acknowledged the problem internally, while also taking responsibility for not doing more to remedy the issue.

“We suck at dealing with abuse and trolls on the platform and we've sucked at it for years, Costolo wrote in an internal memo obtained by the Verge. “It's no secret and the rest of the world talks about it every day. We lose core user after core user by not addressing simple trolling issues that they face every day.”

His blunt remarks were in response to a post on an internal board about Lindy West, a woman that shared her stories of harassment on Twitter with the Guardian, as well as NPR’s This American Life.

Costolo acknowledged Twitter’s problem with harassment while also pledging to do more to combat it.

“I take full responsibility for not being more aggressive on this front,” Costolo wrote. “It's nobody else's fault but mine, and it's embarrassing. We're going to start kicking these people off right and left and making sure that when they issue their ridiculous attacks, nobody hears them.”

Responding to criticism that the platform’s harassment reporting process was too convoluted, the company overhauled it in December. But even with those improvements, users continued to face harassment as well as threats of sexual assault and death threats.

It has led to some celebrities temporarily leaving the service or deleting its app from their phones, including “Girls” creator Lena Dunham, and Zelda Williams, who was harassed on Twitter and Instagram after the death of her father, Robin Williams.

Twitter is scheduled to release its fourth-quarter earnings today after markets close. The company is expected to discuss its performance and business deals. But following the leak of his remarks, it's likely to also face questions on what it plans to do to fight trolls and keep users on the platform.