Interesting, thanks! That is different to the story i remember, but it's possible that i remember incorrectly, or read an incorrect explanation.

I believe that i read about this episode in Hans Moravec's book 'Mind Children'. I can see in Google Books that chapter 5 is on 'Wildlife', and there is a section 'Spontaneous Generation', which promises to talk about a "software parasite" which emerged naturally in the ARPAnet - but of which the bulk is not available:

https://books.google.co.uk/books?id=56mb7XuSx3QC&lpg=PA133&d...