WHAT IS MALWARE IN COMPUTER?

Malware is the collective name for a number of malicious software variants, including viruses, ransomware, and spyware. In another way, we say that Malware is any software intentionally designed to cause damage to a computer, server, client, or computer network.

A wide variety of malware types exist, including computer viruses, worms, Trojan horses, ransomware, spyware, adware, rogue software, wiper, and scareware.

Malware can also be installed on a computer "manually" by the attackers themselves, either by gaining physical access to the computer or using privilege escalation to gain remote administrator access. 

Another way to categorize malware is by what it does once it has successfully infected its victim's computers. There is a wide range of potential attack techniques used by malware:

• Spyware is defined by webroot cybersecurity as "malware used for the purpose of secretly gathering data on an unsuspecting user." In essence, it spies on your behavior as you use your computer, and on the data, you send and receive, usually with the purpose of sending that information to a third party. A keylogger is a specific kind of spyware that records all the keystrokes a user makes—great for stealing passwords.
• Adware is malware that forces your browser to redirect to web advertisements, which often themselves seek to download further, even more, malicious software. As The New York Times Notes adware often piggybacks onto tempting "free" programs like games or browser extensions.
• Ransomeware is a flavor of malware that encrypts your hard drive's files and demands a payment, usually in Bitcoin, in exchange for the decryption key. Several high-profile malware outbreaks of the last few years, such as Petya, are ransomware. Without the decryption key, it's mathematically impossible for victims to regain access to their files. So-called scareware is a sort of shadow version of ransomware; it claims to have taken control of your computer and demands a ransom, but actually is just using tricks like the browser redirect loops to make it seem as if it's done more damage than it really has, and unlike ransomware can be relatively easily disabled.
• Cryptojacking is another way attackers can force you to supply them with Bitcoin—only it works without you necessarily knowing. The crypto mining malware infects your computer and uses your CPU cycles to mine Bitcoin for your attacker's profit. The mining software may run in the background on your operating system or even as JavaScript in a browser window.
• Malvertising is the use of legitimate ads or ad networks to covertly deliver malware to unsuspecting users’ computers. For example, a cybercriminal might pay to place an ad on a legitimate website. When a user clicks on the ad, the ad's code either redirects them to a malicious website or installs malware on their computer. In some cases, the malware embedded in an ad might execute automatically without any action from the user, a technique referred to as a “drive-by download.”