VIRUS (spread with user action)
A virus is a self-replicating program that produces its own code by attaching copies of it onto other executable codes.
Some viruses affect computers as soon as their codes are executed; others lie dormant until a predetermined logical circumstance is met.
A computer virus attaches itself to a program or file enabling it to spread from one computer to another, leaving infections as it travels.
The biggest danger with a worm is the capability to replicate itself on your system, so rather than your computer sending out a single worm, it could send out hundreds or thousands of copies of itself, creating a devastating effect.
A blended threat is a more sophisticated attack that bundles some of the worst aspects of viruses, worms, Trojan horses, and malicious code into one single threat. Blended threats can use server and Internet vulnerabilities to initiate, then transmit and also spread an attack.
The attacker would normally serve to transport multiple attacks in one payload.
An Attacker can also launch a Dos attack or install a backdoor and maybe even damage a local system or network systems.