A host of websites including LinkedIn, Zoom and Downdetector went offline on Friday morning after fresh problems at Cloudflare – the company’s second outage in less than a month.

Cloudflare said the outage came after it adjusted its firewall to protect customers from a widespread software vulnerability revealed earlier this week, and was not an attack. Earlier, it noted a separate issue reported with its application programming interfaces.

The issue lasted for half an hour and was resolved shortly after 9am GMT, it said. This follows a far larger Cloudflare outage in mid-November that hit sites such as X, OpenAI and Spotify as well as multiplayer games such as League of Legends.

That was caused by “a configuration file that is automatically generated to manage threat traffic” growing beyond its expected size and triggering a crash in the software system that handles traffic for a number of Cloudflare services.

Friday’s error appeared far more minor, affecting sites including Canva, Shopify, the Indian-based stockbroker Groww, as well as LinkedIn, Zoom and Downdetector, a site used to monitor online service issues. The Downdetector website recorded more than 4,500 reports related to Cloudflare after returning online.

Given the high-profile series of internet outages in the past months, it could cause some companies to reflect on how they use Cloudflare’s services.

Steven Murdoch, a professor of computer science at University College London, said: “I think people will start asking questions now that there have been these two outages in a short period of time. They’re not very happy, and Cloudflare isn’t very happy either – they’re apologetic. But it’s too early to say whether there’s a systemic problem, such as bad software practices, or it’s just bad luck.”

He said Cloudflare, a global cloud services and cybersecurity firm, marketed itself on the basis of its reliability. Companies use it because it offers a level of immunity to certain kinds of cyber-attacks and can improve the performance of websites, making them faster and more resilient to server crashes.

Its recent outages in the past months, as well as an Amazon Web Services outage in October that affected more than 2,000 companies worldwide, have fuelled conversation among experts about whether key internet services are too centralised and thus vulnerable.

“There’s a huge amount of centralisation,” Murdoch said. “Cloudflare do have a good product, that’s why so many people use them, but it leads to vulnerabilities.”

Michał “rysiek” Woźniak, a DNS and internet infrastructure expert, said: “This again shows how brittle is the big tech internet. This is the fourth major global outage, large enough to be noticed by non-technical media and affect regular people around the world, since 20 October.”

Cloudflare claims that about 20% of all websites use some form of its services. It has nearly 300,000 customers operating in 125 countries, and claims to block billions of cyber-attacks for these users daily. It makes more than $500m (£440m) a quarter.

Woźniak said its recent outages called into question Cloudflare’s marketing, based on its reliability and resilience, and the broader narrative that large companies were safer partners than smaller infrastructure providers.

“These companies have become too big to not fail. And because they handle so much traffic, when they do fail, this immediately becomes a massive problem,” he said.

Murdoch, however, said there could be an upside to this outage for Cloudflare. “When AWS went down, their share price went up, because people realised how many people are using them. In some ways [the outage] is great marketing, because you see how many people are using Cloudflare.”