Malware is intrusive software that is designed to damage and destroy computers and computer systems. The word Malware comes from “malicious software.” In the 1980s the first malware was created which is a computer program code that acts as a host within a computer system.

Some common types of malwares:

Viruses: A virus is a malicious software attached to a document or a file That executes its code and spread from Host to Host. Their code is designed in such a way that once opened, it will disrupt the system’s ability to work, hence creating an operational issue or Data loss.
Worms: Computer Worm malware usually spreads copies of itself from computer to computer, often via email contacts of the victims.
Trojan viruses: Malware software is often disguised as a legitimate tool designed to gain access to user data.
Spyware: Spyware is disguised software that gathers information about a person or an organisation.
Adware: It is spyware disguised as an advertisement which when clicked or opened injects viruses or trojans into the system which can attack a computer system or sometimes redirects you to some other unsafe sites.
Ransomware: Ransomware is malicious software that gains access to sensitive information within a system, encrypts that information so that the user cannot access the system and then usually demands a financial pay out for the data to be released.

Most destructive malwares of all time:

EMOTET: It is a Trojan Malware that is created to target the banking landscape which can sneak into a computer system and steal sensitive and private information. It is also called as malspam which enters into a system mostly through emails, especially spam mails. It is regarded as one of the destructive malware by the Department of homeland security, US. It has affected government and private, Individuals and Organisations alike costing up to one million for each attack.
WannaCry:  This is a Kind of Malicious software mostly used by cybercriminals to extort ransom. This ransomware can encrypt the valuable files of a system or an organisation’s IT structure, further takes control of your system and data as hostage to make it redundant until it is unlocked by the attacker. In 2017 this ransomware created a global cyber epidemic, which affected almost all windows devices.
Petya/Not Petya: NotPetya is considered one of the world’s worst cyberattacks that came into force in 2017. Petya is a family of encrypting ransomware that was first discovered in 2016 – a piece of criminal code that surfaced in early 2016 and extorted victims to pay for a key to unlock their files. This ransomware cost around $10 Billion.
Stuxnet/worm: Stuxnet is a computer worm that was originally aimed at Iran’s nuclear facilities and has since mutated and spread to other industrial and energy-producing facilities. The original Stuxnet malware attack targeted the programmable logic controllers (PLCs) used to automate machine processes.
Zeus trojan: Zeus trojan was primarily created to target financial and banking information. It is also called crimeware. This virus was first caught in 2007 when stealing sensitive information from a system owned by the US state department. This usually uses phishing campaigns, spam campaigns, and drive-by downloads to enter into a target system.
Storm Worm: Storm worm belongs to the botnet family virus. In 2007, It spread to one million computers. Storm worm combined several kinds of attacks, making it far more sophisticated. It majorly targeted Microsoft Windows devices. It accounted for 8% of all malware infections globally.
Mydoom worm: This email worm was first discovered in 2004. It became one of the fastest spreading email worms to date.
SQL Slammer: Found in 2003, this computer worm has caused great devastation in the cyber world leading to a denial of service on some Internet hosts and dramatically slowing down the general internet traffic. It spread rapidly, infecting most of its 75,000 victims within ten minutes.