Final answer:
The 'I Love You' virus was notorious for its rapid spread by generating and sending massive numbers of emails through victims' contact lists, which resulted in significant network congestion and disruptions.
Step-by-step explanation:
The I Love You virus caused harm primarily because C. It generated large numbers of emails that bogged down many networks. This virus was a computer worm that once opened, replicated itself and sent copies to every contact in the victim's Microsoft Outlook address book. This led to an overwhelming amount of email traffic which disrupted systems and networks worldwide. It also overwrote files, including documents and images, potentially leading to data loss, although the major issue was the network disruption it caused.