Over a two-week period, the computer networks at more than half of the Fortune 500 left a remote access protocol dangerously exposed to the internet, something many experts warn should never happen, according to new research by the security firm Expanse and 451 research.

Why it matters: According to Coveware, more than 60% of ransomware is installed via a Windows remote access feature called Remote Desktop Protocol (RDP). It's a protocol that's fine in secure environments but once exposed to the open internet can, at its best, allow attackers to disrupt access and, at its worst, be vulnerable to hacking itself.

What is RDP: RDP is a way of offering virtual access to a single computer. It allows, for example, an IT staffer in one office to provide tech support for a baffled user in a different office.

But RDP is best used over a secured network rather than over the open internet.

"We compare exposed RDP to leaving a computer attached to your network out on your lawn," Matt Kraning, co-founder and CTO of Expanse, told Axios.

It's an opinion shared by experts at McAfee and Sophos, who note that in the absence of multifactor authentication, the protocol can often be hacked into with only a few hours guessing common passwords.

Even in ideal circumstances, when passwords are strong, a malicious actor could overwhelm an RDP connection with traffic (known as a DDoS attack).

What they found: The Expanse/451 study found that 53.4% of Fortune 500 companies had an RDP exposure over a two-week period scanning for open RDP ports.

The technical sophistication of the companies didn't seem to have much impact on RDP exposures. For example, around 80% of hospitality industry companies and just under 80% of defense and aerospace companies had at least one exposure, even though defense and aerospace are among the most security-conscious sectors.

Cybersecurity budget, either as a percentage of the annual budget or total spending, also had no consistent effect on exposure. By percentage of budget, 43% of companies in the lowest-spending quartile had exposures, compared to 53% of those in the top spending quartile.

The bottom line: The threat of RDP exposures often fly under the radar. "IT staffs are really good at looking at what they know about, but not at what they don’t," said Kraning.

"If Fortune 500 companies have exposures, what chance do smaller companies have," he added.

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