Which incident is NOT associated with the year 1999?

The incident associated with the Chernobyl disaster does not relate to the year 1999 as it occurred in 1986. The Chernobyl Nuclear Power Plant experienced a catastrophic accident on April 26, 1986, leading to one of the worst nuclear disasters in history. This event resulted in significant environmental contamination and health issues, and it has been the subject of extensive study and analysis in the context of emergency management and disaster response.

In contrast, both the ILoveYou and Melissa viruses were significant cybersecurity incidents that emerged in 1999. Melissa was one of the first major email viruses that spread rapidly through Microsoft Word documents, while the ILoveYou virus was a worm that propagated via email and caused substantial damage worldwide by overwriting files and sending copies of itself to the victim's contacts.

Given this context, the distinction of Chernobyl as the only event not connected to 1999 makes it the correct answer to the question.