Aye, it happened to me some yonks ago when we used to employ my entirely loveable nephew as a baby squasher.
One morning after a night before, I discovered the wonderfully titled self-replicating "Achtung! Sex Party" dialler all over the computer, including a robust presence on the desktop, potentially linking to a mega-premium dial-up number, had we not been on cable modem.
As I recall, he did say his goodnights and leave promptly that evening...
I graduated to Chameleon porn some time ago, and I've never looked back. It's the real McCoy.
Speaking of Mc's, have you seen the picture series of Gauge Chameleon on a number of clan tartans? RAR!
RE: robust presence on the desktop
I've seen one like that - very graphic name and couldn't be deleted or even renamed despite using many tools / techniques (inc booting to DOS from a floppy and dtrying to delete it manually)
in the end we used the mouse to 'throw' it off the bottom of the screen and so not have it visible - it's gone now though, new hard-drive and fresh OS install.