Just last month, a major cyberattack brought down the likes of Twitter, Soundcloud, Spotify and Airbnb for a few hours. Interestingly, rather than directly attacking the infrastructure of these companies, the assault targeted the domain name system (DNS) host Dyn, which is relied upon by the sites above. This is how a single attack could bring down so many sites at once.
(As you may already know, DNS a bit like the yellow pages of the Internet - but rather than mapping people's names to phone numbers, it maps domain names to IP addresses, which computers require to communicate. Hence, if the DNS provider of a site is down, it cannot be accessed by its users.)
One might imagine that pulling off an attack of this magnitude would require extreme sophistication. In practice, the disruption was caused by a rather rudimentary Distributed Denial of Service (DDoS) attack that overwhelmed the DNS servers of the aforementioned sites.