F-Secure said in a statement that the flaw had nothing to do with the Spectre and Meltdown vulnerabilities recently found in the micro-chips that are used in almost all computers, tablets, and smartphones today.
Rather, it was an issue within Intel Active Management Technology (AMT), "which is commonly found in most corporate laptops, (and) allows an attacker to take complete control over a user's device in a matter of seconds," the cybersecurity firm said.
"The issue potentially affects millions of laptops globally."
The flaw was of "an almost shocking simplicity, but its destructive potential is unbelievable," said F-Secure consultant Harry Sintonen, who discovered it.
"In practice, this flaw could give a hacker complete control over the affected laptop, despite the best security measures."
An attacker would initially need physical access to the device in question.
But once they had re-configured AMT, they could effectively "backdoor" the machine and then access the device remotely, by connecting to the same wireless or wired network as the user, F-Secure said.
In certain cases, the assailant could also programme AMT to connect to their own server, which would eliminate the need to be in the same network segment as the victim.
"No other security measures - full disk encryption, local firewall, anti-malware software or VPN - are able to prevent exploitation of this issue."
A successful attack would lead to complete loss of confidentiality, integrity and availability, F-Secure said.
The assailant would be able to read and modify all of the data and applications a user may have access to on their computer. And they could also install malware on the device, even at the firmware level.
F-Secure expert Sintonen said that organisations needed set a strong AMT password or perhaps disable AMT completely if possible.
The recent discovery of the "Spectre" and "Meltdown" vulnerabilities in computer chips made by Intel, AMD and ARM, have sent big names in the sector - including Amazon, Google, Microsoft and Mozilla - rushing out updates and patches to eliminate the flaw.
Intel said it appreciated the fact that experts were highlighting the issue.
"We issued guidance on best configuration practices in 2015 and updated it in November 2017, and we strongly urge OEMs (original equipment manufacturers) to configure their systems to maximise security," an Intel spokesman told AFP.
"Intel has no higher priority than our customers’ security, and we will continue to regularly update our guidance to system manufacturers to make sure they have the best information on how to secure their data."