One generation viruses(not inherited virus)

[Welwordion]

Well I thought it might be useful if viruses could be created, that  would only effect the bot they were inserted to, this way a parasit bot could insert certain behaviour patterns into another bot  without the fear that the original bot type will not be available anymore. For example battery bots could modify their veggies without  accumulate junk Dna into other veggies.
Also certain genes could be made that only activate or fullfill their task when their is more than one of them in the bots Dna.(like increasing a certain memory value by 3 which is decremented by 4 if >0, if the first gene is doubled
the memory location would become >2 which would be the trigger for a third gene)
And by adding junk genes which will not be copied after reproduction ,bots can learn to camouflage against identification sytems .

[Numsgil]

You can do this, though there is an issue with keeping the virus reproduction code in sync with the virus itself.

Another method would be to code in a condition that only takes effect when the bot sees a baby in front of it, or an enemy bot, or who ever your target is. The danger here is that it's possible the condition will get screwed up by a mutation and you'll get a self replicating virus for real.