Hack question ( Infect spam )

Hello, this is my first post on the forums. I have gone through some threads and there seems to be a lot of helpful members. So I thought I would ask my question here as well ^___^

I have been use hacks occasionally but I never got one that could do what's shown in the picture!

SO..

My question is basically, what hack is this person in the picture using? Infecting an already infected person -Zombie infecting Zombie- over and over? And what hack options should be used to enable that?

Sorry for the inconvenience and thanks in advance!