A few weeks ago, New York City’s 75,000 teachers scrambled to learn how to use videoconferencing services like Zoom as novel coronavirus cases began to rise and schools prepared to close their doors and institute remote learning.

Now, the city’s teachers will have to scramble once more, after Department of Education Chancellor Richard Carranza announced late last night that he had decided to ban Zoom, citing security and privacy issues with the platform.

“DOE staff and service providers should cease using Zoom as soon as possible,” Carranza wrote in an email to principals. He recommended that schools instead use Microsoft Teams, which is compliant with FERPA, the Family Educational Rights and Privacy Act. According to Chalkbeat, the DOE has started training teachers and staff in using Microsoft Teams, and will continue those trainings in the coming weeks.

Use of Zoom among children exploded over the last month, as teachers gravitated toward its simple user experience. With Zoom, students can join a live virtual class from any kind of device, without needing anything more than the classroom’s unique meeting link. Though Zoom wasn’t designed with schools in mind, these features have been a boon for teachers trying to ensure that all students can learn from home, regardless of their family’s ability to provide their child with a new device. Many teachers adopted Zoom after first trying other videoconference services, including Microsoft Teams and Google Meet, and finding them less reliable.

But Zoom also contains a number of critical privacy and security flaws, as educators have been learning the hard way. Anyone with a Zoom meeting link can “Zoombomb” attendees and broadcast inappropriate content, including pornography, depending on settings established by the meeting creator. In some cases, intruders have been able to hijack Zoom users’ webcams. In addition, Zoom’s iOS app has been sharing data with third parties including Facebook, in a potential violation of children’s privacy regulations. Last week, Letitia James, New York’s attorney general, sent Zoom a letter requesting information about its security practices and compliance with state laws governing the protection of student data.

Businesses using Zoom may be able to shrug off such concerns, or hope that government oversight will eventually resolve them. But educators are subject to a more stringent set of rules and parental expectations.

“As more and new kinds of users start using Zoom during this time, Zoom has been proactively engaging to make sure they understand Zoom’s relevant policies, as well as the best ways to use the platform and protect their meetings,” a Zoom spokesperson said in response to a request for comment. “We are proud of the role we are playing during this challenging time and committed to providing educators and other users with the tools they need.”