Viruses

In the 1980s and early 1990s, when very few people had access to the Internet, viruses were not a huge problem. They did exist and did cause just as much damage to computers as modern viruses can today, but there was no fast-moving epidemic because there was no means for a virus to directly infect other computers. Before the Internet, the only way for a computer to be infected was through use of a removable disc that was itself infected. As a result, virus infections were mercifully rare.
All that changed with the widespread growth of the Internet. With near-universal Internet access among computer users in developed countries, and the proliferation of high-speed broadband Internet connections, a virus on one person's computer can infect thousands of other computers. In fact, much of the disruption from virus outbreaks is caused not by the payload of the virus (e.g. deleting hard drive, shutting down computer every five minutes), but by the Internet congestion caused by the virus spreading itself.