Why Doesn’t Computers Get Bacterial Infections?

Why do we use “virus” to describe malicious replicating computer programs? Most of these programs are very complicated and intelligent (comparatively), which resembles more like a bacteria than a virus. Viruses are very simple organisms, very unlike todays “computer viruses”.

We should really say bacterial and even fungal infections (hard and often dangerous to get rid off) for computers.

Anitbiotics (anti-bacterial) offer a wider vocabulary and are graded in different levels. For example Penicillin is a first generation antibiotic while Gatifloxacin is a fourth generation antibiotic. We could use such classification for computer bacterias too.

Thoughts?