Why did God create viruses?

I mean seriously, creepy looking microscopic mockeries of life that can survive for decades without a host patiently waiting to infect anyone who comes near, highjacking your vary cells to produce millions of copies of themselves until the cell itself explodes, spilling the viruses onto the surrounding cells and... show more I mean seriously, creepy looking microscopic mockeries of life that can survive for decades without a host patiently waiting to infect anyone who comes near, highjacking your vary cells to produce millions of copies of themselves until the cell itself explodes, spilling the viruses onto the surrounding cells and restarting the process, corrupting and destroying the very structure of your being from the inside out. Many of them can mutate to be immune to the latest vaccine faster than we can produce it, and no other medicine can stop them. And what constructive purpose do they serve? None whatsoever. They're vile little packages of pure malice that quite literally exist only to destroy.

What sort of disturbed, sadistic bastard god would deliberately create such a thing?
Update: @Daniel@ Technically speaking, they actually are invincible. Or nigh invisible anyhow.
Update 2: @Daniel@ Also, there's a strain of cancer (not a virus, I know, but similar in behavior) called HeLa that's literally immortal.
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