You could define biological life in a way that includes or excludes viruses, I would suggest, and be right either way.

(Also if a biological virus is alive, is a computer virus alive? It's self-replicating and has DNA in the form of code.)

Fundamentally life is a thermodynamic machine. Takes energy and converts a portion of it to 'work'.

Under homeostatic control. There are feedback systems that maintain the integrity of the organism.

In theory has a way of reproducing. This more applies to the species as a whole. Since individuals incapable of reproducing are none the less alive.

Viruses only meet the last and weaker criteria in my book.

Viruses are just replicators. Grey/Green/Brown/Bio goo. They are just dumb machines made by brute-forcing (fuzzing) more complex machines' immune systems.

Viruses might be a different branch on the RNA-replicator tree. Probably when the first replicators started some found - again via brute-forced mutations - that there are some replicators that they can take advantage of to replicate themselves.

And it just seems that closing this security hole is neigh impossible as long as we don't start to seriously tinker with that low level of "life" (eg. cellular machinery, transport, nucleus, messenger and transcription security).

One of the dominant theories for how eukaryotic organisms evolved (and by extension multicellular life) is by incorporating viruses and other prokaryotes internally and there's evidence a variety of viruses permanently entered the gene pool of several animals that were theoretically naturally selected for. It's less a branch and more a mobius rat's nest.

But that's no different how the rest of biology works. A parasite like Giardia is relatively just a dumb machine brute forcing itself through my immune system.

It's very likely an invariant of complexity. Trade offs (and friendly turtles) all the way. And of course evolution doesn't optimize for QALY at all. So it's not surprising that it hasn't really spent much resources on closing the gap. And now we try to do it because we do find it a better goal than "just" thriving in every imaginable niche on whatever complexity it's possible. (We want to maintain our complexity plus occupy more niches.)

https://en.wikipedia.org/wiki/Adeno-associated_virus#Infecti...

A virus needs a host like any parasite, without the host many parasites would not be able to reproduce.

To be pedantic, all you need is at most two (or three, maybe?) of the right gender to reproduce in a vacuum (metaphorically) to make it a living organism. A virus can't reproduce with another virus that way because it can't do anything on its own other than float around waiting for a host, no matter how many strains you mix it with. The host does the actual reproducing for the virus.

Cells can repeatedly produce certain proteins. For instance, a silkworm can spin out a thread of silk. That doesn't meant that molecules of silk are alive because they are reproducing.

Any parasite that requires its host for reproduction could be said to be a byproduct of the host continuing its biological functions usually at the expense of the host.

Nature draws no clear lines, humans apply taxonomy, any line we draw about what is alive and what isn't will be arbitrary.

My opinion is a virus is alive as it core process is based on how all life on earth operates through DNA/RNA. That is my arbitrary line, a distinct self contained genetic code that continues to replicate and evolve is alive. If that code can no longer continue replicating successfully it is dead.

Potassium cyanide can alter what happens in a cell; that doesn't mean potassium cyanide is alive.