In my case, I tried to hover the mouse over the exploding viruses the fastest I can, but they didn't seem to explode. I guess it could be a consequence of my cursor's speed making the collision hard to detect.
Even tho, I think some visuals are required to explain the mechanics. For example, if the virus is about to explode, a color change (into red or orange, maybe), a size change or even a bomb timer sound could be great to explain what's about to happen. If the virus freezes you, then an ice visual or a frezing sound may work perfect. Your game already has some of these kind of details, but they're important in both the proper events and their antelations.
About stylistic decisions, the backgrounds do a great job emulating that Windows 7 aesthetic, but once the timer and the viruses appear they don't look very cohesive. I think this article may work as a first approach of what I was talking about. Sorry if I can't explain the idea more my myself:
https://en.wikipedia.org/wiki/Windows_Aero
I'm not sure if I reached the boss. There was a moment when a lot of windows popped up, but I just lost the control of the cursor and got really confused on what was happening.