Botnet is widely known as Zombie Army . Botnet is a network of infected computers which is used to spam other target which the knowledge of the owners of computer . Generally an attacker infects large number of computers with malicious scripts like viruses and ultimately uses the infected computer as spammer army known as Botnet .system , just like a robot do. Generally the freeware software , cracks and files download from untrusted source contains malicious files which infects a computer and give a root access to the attacker . An attacker spread generally it to the home based computer system . The zombie administrative user is unaware of such things.
Botnets is one of the greatest threats today . An attacker can use viruses to infect more system and create a large zombie army from which he can perform DDos at very high level and can flood a very high capacitive bandwidth or memory.
An attacker generally targets the system or get those system in their zombie army whose firewall and other protecting services are either not well configured or are not up to mark . Generally they are transmitted through internet ports and protocol attacker programs the zombie army in such a way that attack on a specified host or sometimes on the multiple hosts depending upon the size of the zombie army and intention of the attacker