Wikipedia and other Wikimedia Foundation Web sites went down for hours on Wednesday in a global outage caused by a domino effect of technical problems.
The problems started when Wikimedia servers overheated in the organization's European data center and shut themselves off automatically.
Wikimedia then switched all its traffic to its server cluster in Florida, but the failover process, which involves changing servers' DNS entries, malfunctioned, knocking the organization's sites offline around the world.
"Shortly after we did this failover switch, it turned out that this failover mechanism was now broken, causing the DNS resolution of Wikimedia sites to stop working globally," wrote Mark Bergsma, Wikimedia's operations engineer in a post on Wikimedia's Technical Blog.
Google's YouTube video sharing site also reportedly suffered downtime, going offline on Thursday morning, according to news reports.