In the beginning, there was the TCP/IP packet, designed to withstand a "nucular" attack. It achieved this goal: The UnitedStatesOfAmerica's military has attacked countries but failed to bring down the networks it invented.
However, the packet design for ultimate robustness was not designed for security. When a packet arives, you must guess that it came from who it said it did. So the InterNet's robustness transports malware aggressively.
At any given moment, what percentage of the packets in transport on the internet are malicious?