Coronavirus hit home for most Americans in the last two weeks. At Twitter, it's been front-and-center since January, when the virus first spread out of China and into Japan, the platform's second-largest market. Twitter's leadership responded by spinning up a crisis management team, led by the company's corporate security division.

Like most other companies, Twitter had business contingency plans for a crisis. Usually, though, those crises involve things like power outages in an office or an earthquake that shuts down a region for a few days. Hardly anyone planned for coronavirus: a global pandemic, of unknown size and severity, that could change the working habits of millions of employees all over the world.

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But in January, Twitter didn't know that's where it was headed. So the 20 or so members of the crisis team just kept monitoring the situation, creating documents and having Hangouts meetings where they could share ideas, make plans, and try to figure out what was coming next. "The more they can think down the road, the better off they are, because they're trying not to just react to everything," said Jennifer Christie, Twitter's chief HR officer.

By the end of February, things were more dire and more local: 15 Americans had been confirmed to have the virus, including at least one patient in Northern California. So over leap year weekend, Twitter's crisis management team worked long hours debating a big decision: Should we tell everyone to work from home? They knew social distancing was one of the best things people could do, and they thought Twitter could set an example for the rest of the industry.

Twitter had accidentally been preparing for this moment for years. The company has long believed its future includes a more distributed workforce — Jack Dorsey has even publicly said Twitter's future is not in San Francisco. In recent months, individual teams have experimented with going remote for a week just to see how it works. And since coronavirus became an issue, the crisis management team had been working with divisions inside Twitter to figure out what they'd need to go remote. "This gave us an opportunity to accelerate something where we were already headed," Christie said.

By March 2, CEO Jack Dorsey and his executive team had decided Twitter should start "strongly encouraging" people to work from home. "We said, let's be as proactive as we can: We can react to information that keeps coming out, or we can try to look farther down the road and see where it's going to go," Christie said. "We'd rather risk looking like we were too far ahead than be too far behind."

While Twitter was holed up trying to figure out how to send people home, companies across Silicon Valley were faced with similarly high-stakes decisions. Things took a turn at Slack on March 5, Head of Strategic Communications Jonathan Prince told me, when the company learned an employee had been notified by the CDC that they had recently been in a coronavirus-exposed area. (Prince says this person has now cleared their 14-day period with no symptoms.) The company responded by telling employees they could work from home if they wished, and that the office would be closed for cleaning over the weekend.

That was Wednesday. By Friday, the situation everywhere seemed to be getting worse. "It was becoming increasingly apparent that the smart thing to do, and the responsible thing to do, and the caring thing to do, and the socially responsible thing to do, would be to just move everyone remote," Prince said. Now, this is easier for Slack than most companies. It's Slack. It built a product, and company culture, based on making an app that replaces being at an office. "In some ways, we knew we could handle it, because of how we work together," Prince said. "And we knew it would set a good example, to the extent that's important."

Things moved similarly quickly at Box. The company had spun up its own crisis management team after noting the outbreak in Japan, quickly building a sort of doomsday clock for coronavirus, a three-level understanding of the outbreak and its effect on Box employees.

Level one: There's no outbreak nearby, we're probably fine.

Level two: There are issues nearby, but we're still OK.

Level three: Coronavirus is in the office.

For a week, CEO Aaron Levie said, the leadership team was sending emails to staff with updates. "I think the first day was, 'Hey, work from home if you're feeling sick, or you're worried.' Then it increased in severity from there," he said. Now more than 90% of Box employees are working remotely.

All along the way, Levie was on an email chain with nine enterprise-software CEOs, sharing their latest thinking — along with "Medium articles at different levels of apocalyptic meltdown." Nobody on the thread, Levie said, fought to keep employees in the office.

On March 11, Twitter took an even stronger stand. It told all its employees, globally, to work from home. Company executives wanted to give employees a sense of stability, to keep them from feeling like everything was always changing — even when it was. Making decisions office by office or region by region, Christie said, "would have felt a lot more thrashing to everybody. You'd just be on pins and needles for what's next." Google and others quickly followed suit, telling employees all over the world to work at home for the next several weeks.

Turning your office-based company into a remote one isn't as simple as sending everyone home, though. Employees had to set up home offices and figure out how to work alongside spouses, kids and pets. Scheduled job interviews, upcoming travel, planned conferences all had to be canceled or rescheduled. New employees still needed to be onboarded, all-hands meetings still needed to happen.

And then there are the big, existential questions: Switching to a remote workforce comes with business costs that are hard to understand. "It's definitely been confusing on that front," Levie said, "because you have to balance. We have to support our customers, we have to run a business, but we also have to think about all the worst-case scenarios that could happen." Luckily, he said, because Box works with multiple cloud providers and across many data centers, keeping the service running isn't likely to be a problem.

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The bigger challenge for Box, and for Slack, has been a deluge of people who are suddenly using their services and don't really know how. Slack is doing free, live consultations for anyone trying to get up to speed on remote work — and has gotten so many requests that all Slack employees are being invited to participate in training. "There's been a huge number of volunteers to do that," Prince said. He said everyone senses the magnitude of this moment, and the possibility that Slack can be part of a solution, and wants to help.

Now that so many people are working from home, it gives executives more time to figure out what's next. "This is sort of business as usual for the next couple of weeks," Levie said. "And we'll reevaluate from there." Christie said Twitter is working with vendors and contractors to make sure they're taken care of, as well as preparing for what happens when offices eventually do open again. What if, after weeks or months of working from home, people don't want to go back to the office the same way? Maybe Twitter's offices should have fewer desks and more social spaces — or maybe people will be so tired of working next to their spouses that they'll want quiet workspaces more than ever. Twitter is working on a survey for employees that will dictate a lot of the company's future office plans.

It's still so early in the coronavirus timeline that it's hard to know what's next. Levie told me he'd gotten more than 1,000 emails this week containing the word "covid," and that his schedule is wall-to-wall half-hour phone calls all related in some way to Box's response to the virus. But across all these companies, one thing seems universally true: Everyone's now learning how important it is to prepare for the worst — and that "the worst" may come in a way they never expected.