They aren't alive in the traditional sense. They're just DNA and proteins instead of full cells, have no metabolism of their own and they lack the ability to reproduce autonomously. They do that by hijacking cells and changing the blueprints to replicate more viruses instead of what they originally were gonna create. This process isn't entirely accurate which is why viruses have a comparatively high mutation rate. I guess we kinda know what viruses are but not what to categorize them as. It also doesn't help that we only know a tiny fraction of viruses. Mostly those that cause issues for other organisms. There's what's called the viral dark matter, meaning all the viruses we don't know yet. Nobody can even give a decent approximation regarding the amount of different viruses but it's safe to say more than 99% of viruses have yet to be discovered.