Riday’s technology outage hasn’t just cut off people around the world from their precious files, frozen their bank accounts and grounded their flights home—it’s also taken a huge chunk out of George Kurtz’s fortune.

As Forbes writes, the billionaire co-founder and CEO of CrowdStrike, the cybersecurity company whose software triggered the outage, suffered a major financial loss.

Kurtz’s net worth was down about $300 million as of 3:30 p.m. Eastern on Friday, as shares of CrowdStrike stock are down 11% since Thursday’s close. Forbes estimates that Kurtz, who was worth more than $3.2 billion on Thursday, is now worth about $2.9 billion.

The reason for the drop is simple: Most of Kurtz’s wealth is tied up in CrowdStrike stock. He has been the CEO of the company since its inception in 2012. He owns more than 3% of the company’s shares.

It was a lucrative investment, helping push Kurtz, 53, from a $1.2 billion net worth after CrowdStrike’s 2019 IPO to $3.2 billion before Friday’s collapse, as the stock has more than quadrupled in value over the past five years amid a growing need for cybersecurity.

Annual recurring revenue topped $3.4 billion as of January 31.

Then came the disastrous software update sent out early Friday. While trying to send an update from the popular Falcon Sensor product, a cloud-based method for performing cyber security functions, CrowdStrike sent a flawed file that ended up crippling millions of Microsoft computers around the world.

The outage continued, rendering Windows devices unusable as CrowdStrike and the tech world worked to get their operations back on track.

The company released a statement Friday, and Kurtz tweeted: “CrowdStrike is actively working with customers affected by a flaw identified in a content update for Windows hosts. … This is not a security incident or a cyber attack.”

The issue has been identified and a fix has been shared, CrowdStrike wrote in the statement. CrowdStrike stock fell in after-hours trading and opened Friday down 15% before recovering slightly. Kurtz did not respond to a request for comment for this story.

Who is Kurtz?

Kurtz, a native of Parsippany, New Jersey, did not grow up rich. He studied accounting at Seton Hall University and then spent nearly a decade at consulting firm PWC and accounting giant Ernst and Young, much of it working in cybersecurity-related roles. He was one of the first five employees to be hired full-time in a cybersecurity position at PWC.

In 1999, he founded the security consulting firm Foundstone in 1999. He sold the company, staffed by a team of former EY colleagues, to cybersecurity giant McAfee in 2004 for $90 million, according to Kurtz’s LinkedIn.

After joining McAfee as a senior vice president, he worked his way through the ranks and, in 2009, became chief technology officer. He founded CrowdStrike in 2012 and took it public on Nasdaq in 2019. Along the way, the company has made a name for itself, including by investigating the Russian intelligence hack of the Democratic National Committee in 2016. CrowdStrike was added to the S&P 500 Index last month.

Despite a big drop in his fortune on Friday, Kurtz – a low-key billionaire who lives in Paradise Valley, Arizona with his wife and two children – he remains very rich.

In addition to owning roughly $2.5 billion in CrowdStrike stock at current prices, he has sold off hundreds of millions of dollars worth of stock over the past five years to add to his bank account. And he’s an accomplished race car driver who won the LMP2 class at the 24 Hours of Le Mans in 2019. CrowdStrike is the “official cyber security partner” of the Mercedes-AMG Petronas Formula 1 team, which was also hit by the outage on Friday. .