A Zoom Video Communications Inc. outage Monday ground some work meetings and online learning to a halt on the first day of class for many U.S. students, highlighting the vulnerabilities of virtual school during the coronavirus pandemic.

Webinars and other online meetings were disrupted or inaccessible until around 1 p.m. in New York, the San Jose, California-based company said in a tweet. Users also couldn’t sign up for paid accounts, upgrade or manage their service on Zoom’s website. The software maker didn’t disclose the cause of the technical difficulties.

Zoom’s downtime demonstrates how the stakes of technology glitches have changed during the Covid-19 pandemic, when people have to remain home to reduce the spread of the virus. In the past, occasional outages might have prevented people from updating their social media status or seeing friends’ new posts at worst. But now, communications tools dictate whether children can learn and employees can work. In the coming weeks, millions more kids in the U.S. will be going back to school online, in person or through a hybrid of the two -- putting additional stress on Zoom and other videoconferencing tools.

It’s another reminder of the tremendous responsibility entrusted to a small company most Americans had never heard of eight months ago and that has little experience being a mission-critical tool for as many as 300 million meeting participants a day. The coronavirus thrust Zoom into the spotlight and broadened its appeal beyond the original target of office users. Earlier this year, Zoom suffered a series of controversies related to privacy and security.

The shares fell 2.6% in intraday trading to $282.15 at 3:25 p.m. in New York. The stock has quadrupled this year because of surging customer demand.

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