Zoom Video Communications Inc raised its annual revenue forecast by more than 30 percent after comfortably beating quarterly estimates on Monday as it converts more of its huge free user base to paid subscriptions.

Shares of Zoom, which have surged almost four-fold this year, rose by 9.3 percent to 355.30 U.S. dollars after the bell. Earlier in the day they hit a record closing high of 325.10 U.S. dollars in regular trading.

Video-conferencing platforms, once used mostly as a technological substitute for in-person meetings, became a vital part of day-to-day life this year for people stuck at home under coronavirus restrictions, be it for work, school or socializing. Zoom rivals such as Microsoft Corp's Teams and Cisco System Inc's Webex, have also seen soaring usage.

When the pandemic hit in early 2020, Zoom was a relative upstart founded by a former Cisco executive that had gone public on a promise to make video conferencing software easier to use. But the ease of use came with privacy and security concerns that drove some customers to competitors earlier this year and prompted Zoom to embark on a 90-day plan to address the issues. Zoom began testing end-to-end encryption of its service in July but has not yet implemented the feature for most users.

The surge in usage also strained Zoom's infrastructure, with some outages last week as schools in many parts of the United States resumed classes virtually.

Since the start of the pandemic, Zoom has worked to convert the mass of free users into paying customers, which is important because the company relies on both its own data centers and cloud providers such as Amazon.com and Oracle Corp to provide its serving, meaning it must bear costs for free users.

The company said revenue rose by 355 percent to 663.5 million U.S. dollars, topping analysts' average estimate of 500.5 million U.S. dollars. The company's gross profit rose to 71 percent from 68 percent, but remains far below the 80 percent range Zoom operated at before free users flocked to the service.

Zoom said it now has 370,200 institutional customers with more than 10 employees, up about 458 percent from the same quarter last year. The number of large customers - those generating more than 100,000 U.S. dollars in revenue in the past year - more than doubled to 988 in the fiscal second quarter.

Zoom is working to expand its service in India, where it opened a technology center in Bengaluru last month, and plans to launch a large teleconferencing screen to work with its service, a challenge to companies like Cisco that sell both software and hardware for video calls.

The company, founded and headed by former Cisco manager Eric Yuan, raised its annual revenue target for fiscal year 2021 to a range of 2.37 billion U.S. dollars to 2.39 billion U.S. dollars, from 1.78 billion U.S. dollars to 1.80 billion U.S. dollars previously.

Net income attributable to common stockholders rose to 185.7 million U.S. dollars, or 63 cents per share, from 5.5 million U.S. dollars, or 2 cents per share, a year earlier.

Excluding items, the company earned 92 cents per share, beating the average analyst estimate of 45 cents, according to IBES data from Refinitiv.