Why are websites and apps not working? WhatsApp, Facebook, Instagram, Etsy and USPS taken down amid major outages

Many of the world's biggest websites have stopped working, in what appears to be a linked outage taking place across the world.

Facebook, Instagram, WhatsApp, Etsy and the website of the US Postal Service are all being hit by problems. Others such as Twitter and WhatsApp also appear to be having some issues.

It is not clear what is causing the issue, which is only hitting specific users in some reasons. It is also not confirmed how or if the issues are connected.

Facebook acknowledged the problems, though did not give any detail on how they might have been caused.

"We’re aware that some people are currently having trouble accessing the Facebook family of apps," it wrote on Twitter. "We’re working to resolve the issue as soon as possible."

In 2016, an infamous attack on one part of the internet that served online content for many of the world's biggest websites meant that much of the internet – including Reddit, Spotify and Twitter – stopped working. That was later connected to a botnet, which took control of huge numbers of household internet devices without their owners knowledge and pointed them at one part of the internet, taking them offline.

Such an attack is known as a distributed denial of service attack and can quickly break large parts of the internet's infrastructure by overloading it with traffic.

Because many of the world's largest internet companies rely on the same underlying infrastructure, a single point of failure can instantly cause issues across much of the web. Problems at Google Cloud and Amazon Web Services, for instance, have in the past caused major issues for many of the biggest websites.