At this point the infected computer is under the control of the malware author or his/her command and control system.
The next step is to spread to gain more systems under the control of the malware author. The initial infection mechanism, or Vector, can be reused or the malware can spread through other mechanisms.
Once inside a network, for instance a company or home network, the malware may spread through network sharing or direct exploitation that was not possible with firewalls, IDS/IPS, malware gateways and other protection mechanisms that were present initially.
Sometimes the malware does not look inward towards the network it is on but rather looks outwards at other systems, either by being an attack mechanism (spam bots, DDoS zombies, etc…) or by spreading the attacks via online services such as posting malware links to sites and hijacking social networking sessions to spread malware links or exploits.
The propagation mechanisms are one of the primary components that define the genealogy of malware, sometimes being named for its method or a characteristic of it.