There is also unplanned downtime, occurring unexpectedly, most often due to defective components, software crashes (also caused by viruses), natural disasters, power failures, disruptions at the internet provider, or human error. According to the Visible Ops Handbook of the IT Process Institute, 80% of unplanned failures are due to poorly planned changes or incorrect configurations made by IT administrators.
Unplanned downtime can also happen during DDoS (Distributed Denial of Service) attacks. During a DDoS attack, hackers send enormous amounts of bandwidth to a server, slowing it down or blocking it completely.
DDoS attacks are becoming increasingly common. According to NBIP, a joint venture between internet providers, the number of DDoS attacks has sharply risen in recent years. In 2018 this number grew by 15% compared to the year before. ING and ABN AMRO, for example, became victims of DDoS attacks several times. The servers became overloaded, affecting consumers, online stores, and services.