On which day did ARPANET suffer a 4 hour long network crash?

Arpanet suffered a 4-hour-long network crash on October 27, 1980. The crash was primarily caused by a software bug in the network's IMP (Interface Message Processor) system. This bug led to a chain reaction of events, resulting in a complete network outage for several hours. It was a significant incident in the history of computer networking, highlighting the vulnerability of early computer networks and the need for improved reliability and robustness in network infrastructure.