Yes, I know virii is incorrect. It just sounds so cool, though.
Anyways, this virus, designed for 2.4.3, will make veggies spread it but not be killed by it, and other bots will die quickly if they receive it. It uses some fancy condition-less logic. Make sure to write in some sort of condition to prevent it from killing your bots.
cond
start
*.thisgene .mkvirus store
*.myeye *.myshoot add 32000 mult 50 add 32000 ceil .vshoot store
.delgene dec
stop