A cyber attack on Wikipedia forced the website offline in several countries on Friday.
The online encyclopedia stopped working for users across Europe, and a number of places in the Middle East.
Wikipedia failed to load on desktops, tablets and mobile phones.
Outages were reported shortly before 7pm, BST, according to the downdetector.com , which monitors websites.
“Wikipedia was hit with a malicious attack that has taken it offline in several countries for intermittent periods,” a spokesperson said late on Friday night.
“The attack is ongoing and our Site Reliability Engineering team is working hard to stop it and restore access to the site.
“As one of the world’s most popular sites, Wikipedia sometimes attracts “bad faith” actors. Along with the rest of the web, we operate in an increasingly sophisticated and complex environment where threats are continuously evolving.”
The spokesperson added: “We condemn these sorts of attacks. They’re not just about taking Wikipedia offline. Takedown attacks threaten everyone’s fundamental rights to freely access and share information.
“We in the Wikimedia movement and Foundation are committed to protecting these rights for everyone.”
“The Wikimedia server...is currently being paralysed by a massive and very broad [distributed denial of service] attack,” read a tweet posted during the outage on Wikimedia’s German Twitter account.
A distributed denial of service [DDOS] attack occurs when a huge network of computers all try to access a certain website or internet service at the same time, causing it to collapse under the strain of too much traffic.
The majority of the computers used in these attacks are ‘bot’ computers - ordinary personal computers that have been infected with malware, putting them partially under the control of hackers.
These networks, or ‘botnets’, can be made up of tens of thousands of computers, which have been compromised by malicious hackers without the knowledge of their owners.
When an attack begins, the hackers in charge of a botnet issue instructions to all the computers to access a certain website at the same time, repeatedly.
Bombarded by massive amounts of traffic, a website can collapse.
Wikipedia also suffered an outage affecting hundreds of users in September 2017.
The online encyclopaedia is used widely across the world.
There are Wikipedia sites in 300 different languages, with some 46 million articles accessed by 1.4 billion unique devices every single month, according to figures from 2018.
Wikimedia is a charitable foundation that runs entirely on donations.
There are fewer than 400 full-time staff working for the foundation worldwide.
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