On Zoom, there is a default setting that allows any meeting participant to share their screen without permission from an event’s host. Anyone who has a link to a public meeting can join. Links to public Zooms are traded in Facebook Groups and Discord chats, and are easily discoverable on Twitter and public event pages.

“We have been deeply upset to hear about the incidents involving this type of attack. For those hosting large, public group meetings, we strongly encourage hosts to change their settings so that only they can share their screen. For those hosting private meetings, password protections are on by default and we recommend that users keep those protections on to prevent uninvited users from joining,” said a spokesperson for Zoom Video Communications in a statement.

The post included tips for users seeking to “keep the party crashers” out of their videoconferences, including limiting screen-sharing to certain participants and making events invitation-only.

Zoom has seen a sharp rise in use over the past few weeks. On Sunday nearly 600,000 people downloaded the app, its biggest day ever, according to Apptopia, which tracks mobile apps. The company is currently valued at $29 billion.

But the platform was built as an enterprise technology tool, not a consumer social tool. As such, the company was not prepared to moderate user behavior as other social networks do.

“With much broader adoption, abuse and misuse will follow, so Zoom should be getting ready to handle reports and complaints,” Jules Polonetsky, the chief executive of the Future of Privacy Forum, recently told The Times.