Why did huge swathes of the internet suddenly go offline yesterday?

A computer programming language supporting an estimated 70 per cent of all websites was found to have ‘critical vulnerabilities’

Thu Oct 22 2026 - 15:49 • 4 MIN READ

It caught countless website developers off guard and has left many wondering how protected their cyber systems really are.

When the team behind computer programming language PHP issued a warning to its users, an estimated 70 per cent of all websites, that “critical vulnerabilities” were found in its software, it sent the internet into a digital frenzy on Tuesday.

“Who is at risk: all PHP installations serving web requests”, the developers put it bluntly, but not so simply – “all installation serving web requests” means, in layman’s terms, a website that you can click on.

Users were advised to update immediately or go offline to avoid suffering a cyberattack. While the bug has largely been exterminated nearly 24 hours after it was first spotted, the fright it has caused will not be easily forgotten.

Firstly, what is PHP?

“It’s essentially a framework that websites run on,” says Martin Potgieter, the chief technology officer for the South African arm of Integrity 360, a Dublin-based cybersecurity specialist consultancy firm.

[ Revolut’s outage was a warning to us allOpens in new window ]

While it’s difficult to say just how many websites run on it, estimates hover around 70 per cent. “A large number of websites on the internet are using it,” Potgieter says.

“It’s an open source code, that’s why it’s so extensively used,” he continues, “many people might say ‘oh, well, it’s an open source code so that’s why it’s insecure’, but that’s not really the case – it doesn’t make it less secure, just more available”.

And what happened to it yesterday?

“A flaw was found in the software that renders the websites using PHP vulnerable to an attack,” Potgieter says. “Once that flaw was discovered, it’s essentially a race between the PHP developers trying to create a patch quicker that news can get out and the details to exploit that vulnerability get out to the world.”

[ ‘Critical vulnerabilities’ found in computer code supporting up to 70% of internetOpens in new window ]

A “patch” is a corrective measure used to eliminate errors or issues within codes. “It’s very similar to when you get a little notification on your laptop that says Microsoft needs to do updates,” Potgieter goes on. “It’s essentially a change to the code that renders the vulnerability inoperable.”

“Many people were advising to switch off your website, if you can’t patch it, because patching does take time”, he says.

And thus, countless websites suddenly went offline for fear of a cyberattack. You couldn’t read an article from the Journal, you couldn’t buy a screwdriver from Woodie’s DIY and you couldn’t even access the Finnish government’s land registry records.

Why is motor insurance so expensive in Ireland?

Listen |

32:56

Well, how serious is this?

“It is quite serious,” Potgieter says.

“If a hacker successfully exploits the vulnerability, they can take control of that system and do what they want with it. That’s obviously high risk – they could take information off of the system or use it for another attack,” he continues.

“There were reports of attempts to exploit the vulnerabilities ... I’m not sure if there’s any verified reports that they were successful – but it’s only a matter of time,” he says. If successful, hackers could control website operations or harvest users’ data, among other actions.

Brian Honan, a cybersecurity expert and chief executive of BH Consulting, says “it’s not rare for a big vulnerability to be found in a piece of software, but I think the impact of this vulnerability will be a surprise due to the fact that the software is used so widely”.

“The vulnerabilities are of a very high severity and would actually enable a potential attacker to remotely control and manage a website to do what they want with it.” he goes on.

[ More than half of Irish business leaders worried over ‘sophisticated cyber attacks’ by AIOpens in new window ]

“The impact of this is huge,” Honan says, “there are websites that are liable to be taken over.”

And who caught the issue?

Honan says “there’s continuous research by security professionals worldwide into looking for weaknesses in software so that they can go back to vendors and recommend to them how to improve the software and make the platforms more secure.”

“With the advent of AI (artificial intelligence) platforms and tools, that makes the research much more scalable and, in some ways, easier to carry out. Researchers can find more vulnerabilities than they could beforehand thanks to AI.”

OpenAI, the force behind ChatGPT, was quick to take credit. “We led a Coalition of maintainers, researchers and security providers to address critical vulnerabilities in PHP,” the company said in a statement on Tuesday.

“Given the severity of these flaws and PHP’s widespread use, we consider this one of the most impactful security issues in recent memory,” OpenAI said.

But Potgieter is less convinced. “Sometimes, these AI labs take credit for AI being used as part of this research, but in many cases, it wouldn’t be possible without humans either starting the process or guiding the AI through it.”

IN THIS SECTION