Much of the internet appears to be broken. A distributed denial of service (DDoS) attack has taken down systems run by Dyn, Inc, one of the largest providers of internet services in the world. And as a result it seems to be causing problems for a variety of websites – including Reddit, Spotify and Twitter. Dyn runs domain name servers or DNS. They work as a phone book or map to the internet, making sure that when someone writes an address into their computer or phone, it can be directed to the right place and show the right information.