On February 28, questions about the coronavirus swirled around Google's offices. The company was being criticised for YouTube's handling of hoax videos, a major company conference was cancelled and an employee in Zurich tested positive.

Chief executive Sundar Pichai sent a memo reminding thousands of his workers about Google's important role as a provider of timely and accurate information in uncertain times. "You've heard me talk about helpfulness in the context of moments big and small. This is one of those big moments," he wrote.

Since Covid-19 began to spread, Google has aggressively intervened in some of its most popular online services to limit the spread of misinformation. This is a departure for a company that has relied heavily on software and automation to index and rank information throughout its 22-year existence.

Google searches related to the virus now trigger an "SOS Alert," with news from mainstream publications including National Public Radio, followed by information from the US Centers for Disease Control and Prevention and the World Health Organisation displayed prominently.

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In contrast, a recent search for "flu season" showed the website verywellhealth.com at the top, while another search for "flu" produced tweets, including one from US President Donald Trump comparing coronavirus to the common flu.

The coronavirus has killed more than 3900 people out of 113,000 confirmed cases. Online platforms have been inundated with rumours and misinformed concerns about the pathogen as it spread west from Asia, particularly in floods of messages on Twitter, according to Carl Bergstrom, a professor at the University of Washington. Google is swept up in this because it has a deal with Twitter to show tweets in search results, especially for queries about live and recent events. "It's really just a churning mess right now," Bergstrom said.

MAJA HITJI/GETTY IMAGES The coronavirus has killed more than 3900 people.

On YouTube, Google's video service, the company is trying to quickly remove videos claiming to prevent the virus in place of seeking medical treatment. And some apps related to the virus have been banned from the Google Play app store, prompting complaints from developers who say they just want to help.

The company is also giving up revenue. Pichai said in another recent memo that Google has blocked tens of thousands of ads "capitalising" on the virus. It's also pulled ads from YouTube videos that discuss Covid-19, while giving governments and NGOs free ad space on the video service.

"In a highly uncertain, fearful moment there will naturally be more disinformation," said Thomas Rid, a professor of strategic studies at Johns Hopkins University. "Right now, Google should absolutely emphasise results from the government agencies that can be trusted here, from research-based, evidence-based data."

Google stressed that it was not manually changing search results. "Our systems are designed to automatically detect searches that may be related to topics like health and apply the same treatment of elevating reliable and authoritative sources in the results," a company spokeswoman said.

Google has stepped in before, limiting ads on opioid treatment searches for instance. But it often moves slowly and only after many complaints. That approach is becoming less tenable as governments and regulators scrutinise the power of large internet platforms and closely monitor how they deal with misinformation. EU Commissioner Vera Jourova recently warned Google and Facebook Inc. to crack down on false information about the virus.

Even before the coronavirus began to spread, Pichai was overseeing a major overhaul of the company's approach to health care and medical information. He has hired health-care industry executives for a new division that uses Google's artificial intelligence and cloud-computing prowess to develop new revenue from the sector. The coronavirus is the first real test of this initiative.