New York City has banned the video conferencing platform Zoom in city schools weeks after thousands of teachers and students began using it for remote learning.

The education department received reports of issues that impact the security and privacy of the platform during the credentialing process, according to a document shared with principals that was obtained by Chalkbeat on Friday night.

“Based on the DOE’s review of those documented concerns, the DOE will no longer permit the use of Zoom at this time,” the memo said.

Instead, the guidance says, schools should switch to Microsoft Teams “as soon as possible,” which the education department suggests has similar functionality and is more secure.

After initially saying educators should not use Google platforms for video and audio conferencing with students, department officials on Sunday said the platform is safe enough to use.

Schools Chancellor Richard Carranza did not give a specific timeline for schools to stop using Zoom and acknowledged the transition could not happen immediately. “We want people to gradually transition to another format,” he said at a Sunday press conference. “We’re going to do this in a thoughtful manner.”

Still, the change is likely to cause headaches for schools and families, as the use of Zoom became widespread after the city shuttered school buildings on March 16 and moved over a million students to remote learning a week later.

Not all schools use Zoom, though many have since the platform offers a free version and is relatively simple to set up. Last month, the city’s Panel for Educational Policy met via Zoom, a meeting that included Carranza and other top officials.

But the platform has also caused problems for educators and has come under fire nationally for a range of security and privacy issues.

In some cases, students have taken to “Zoombombing” online classes, essentially logging into online classes uninvited and hijacking everyone’s screens with inappropriate images or audio. “Zoombombing is no joke. I don’t think we were ready for that,” Pat Finley, a co-principal at the Metropolitan Expeditionary Learning School in Queens, previously said.

Students have also sometimes flooded the platform’s chat function with inappropriate comments, disrupting virtual instruction.

Despite those issues, some principals said they had already devised solutions and found the decision to ban Zoom puzzling.

“It’s been a huge lift to get this all going,” said one Brooklyn principal, who spoke on condition of anonymity. “It’s taking all the work we’ve done and flushing it down the toilet — and you’re going to lose some kids along the way.”

The biggest concern, the principal said, is that the switch will create an additional barrier for students to access remote learning, a hurdle that may disproportionately affect students with disabilities or families with limited fluency with technology.

A second Brooklyn principal echoed that the change will disrupt remote instruction. “If the DOE follows through with this decision, I believe that the impact will be no more live teaching for many teachers,” the principal said, citing the clunkiness of the Microsoft platform. “I am not sure that the DOE and the mayor fully understand the impact of decisions like this.”

Danielle Filson, an education department spokesperson, said the department has already begun training schools to use Microsoft Teams and will continue that process on Monday.

“We will support staff and students in transitioning to different platforms such as Microsoft Teams that have the same capabilities with appropriate security measures in place,” she said.

Last week, New York Attorney General Letitia James raised concerns about Zoom, including whether third parties could secretly access users’ webcams, reports that the company shares data with Facebook, and whether the company was following state requirements about safeguarding student data.

Zoom takes “its users’ privacy, security and trust extremely seriously” a spokesperson wrote in a statement. “We recently updated the default settings for our education users enrolled in our K-12 program to enable waiting rooms and ensure teachers are the only ones who can share content in class by default.”

The education department’s decision to ditch Zoom raises questions about why the platform wasn’t rigorously vetted before so many schools decided to adopt it; many of the concerns about the platform’s security aren’t new. Some schools asked parents to sign consent forms before they began using Zoom.

It’s unclear how seamless the transition to Microsoft Teams will be. Students and staff can log in to the platform using existing usernames and passwords, and the department has already created Microsoft accounts for all students, officials said. The Microsoft platform does not require separate software to participate in video conferences.

“The DOE also continues to review and monitor developments with Zoom,” the memo continues, “which may be approved for use at a later date.”

Department officials did not answer questions about whether Zoom could be used for purposes that don’t involve students, such as teacher training, or how much money is being spent to transition to Microsoft Teams.