In 1989, Robert Morris created what is now widely acknowledged as the first computer worm. This self-propagating virus spread so aggressively and rapidly that it succeeded in closing down much of the internet. While other subsequent attacks have gained far more notoriety, the Morris worm was a landmark incident in that it was the first widespread instance of a denial-of-service (DoS) attack. Due to the infancy of the internet at the time, the impact was nowhere near as devastating as it would be today. However, it laid the groundwork for the kinds of security issues that we've seen ever since.
The Morris worm and the early nuisance attacks that followed were early instances of having to deal with, and respond to, cyber-security attacks. They ultimately led to the security industry as we know it – including the establishment of CERTs (Computer Emergency Response Teams) as a central point for co-ordinating responses to these kinds of emergencies. The initial reaction from the industry followed the old adage ‘prevention is better than a cure’, giving rise to what has become a litany of preventative and detective security products.