Malware terms

Introduction
Viruses and worms are two well-known types of malicious software. Many threats combine elements from different types of malicious software together,These blended threats don’t fit into any one class, so the term malware, short for malicious software, is used as a catch-all term to describe a number of malicious threats, including viruses, worms, and more. Malware presents arguably the largest security threat to computer
users. It can be confusing to understand what the difference is between a virus and a Trojan, but these explanations should help:

Virus A virus is malicious code that replicates itself. New viruses are discovered
daily. Some exist simply to replicate themselves. Others can do
serious damage such as erasing files or even rendering the computer itself
inoperable.

• For a virus to be successful, it has to be executed on a computer by a human. That means a file has to be opened, a program has to be run, or a computer has to be booted. In other words, programming code has to be run by a human action. That could be you, me, friends, or anyone who uses a computer. This is not to say that anyone executes a virus on purpose. Usually we're tricked into it. But a virus requires a human's help to proliferate. Remembering this fact goes a long way to preventing viruses from ever running amuck on your computer.

Worm A worm is similar to a virus.They replicate themselves like viruses,
but do not alter files like viruses do.The main difference is that worms
reside in memory and usually remain unnoticed until the rate of replication
reduces system resources to the point that it becomes noticeable.

Spyware Spyware is software. And it's not written and distributed to pursue some fancy spy agency agenda, such as finding out the color of Fidel Castro's shower curtain. It's mostly written so its authors can find out about you, where you live, what you like to do on your computer, and where you go on the Web. Why do they care? Because they can make money from that information.

• Spyware is considered malware (malicious software) because it installs itself on your computer without your knowledge. Then it watches your computer habits, compromising your privacy.

• Spyware is also annoying because it pushes unwanted advertising at you. Pop-up ads appear out of nowhere on your desktop. And because it is spying on you, it pushes ads at you that it thinks you'll click on.

• If that's not enough, spyware can clog your system's memory and use space on your hard drive, causing performance slowdowns. It can get so cloggy that it'll make your computer unusable.

Trojan A Trojan horse got its name from the story of the Trojan horse in Greek legend. It is a malicious program disguised as a normal application. Trojan horse programs do not replicate themselves like a virus, but they can be propagated as attachments to a virus.

Rootkit A rootkit is a set of tools and utilities that a hacker can use to
maintain access once they have hacked a system.The rootkit tools allow
them to seek out usernames and passwords, launch attacks against remote
systems, and conceal their actions by hiding their files and processes and
erasing their activity from system logs and a plethora of other malicious
stealth tools.

Bot/Zombie A bot is a type of malware which allows an attacker to gain
complete control over the affected computer. Computers that are infected
with a bot are generally referred to as zombies.