Malicious software, commonly known as malware, is any software that brings harm to a computer system. Malware can be in the form of worms, viruses, trojans, spyware, adware and rootkits, etc., which steal protected data, delete documents or add software not approved by a user.

software that aims to gather information about a person or organization sometimes without their knowledge, that may send such information to another entity without the consumer's consent, that asserts control over a device without the consumer's knowledge, or it may send such information to another entity with the consumer's consent, through cookies ."Spyware" is mostly classified into four types: adware, system monitors, tracking cookies, and trojans examples of other notorious types include digital rights management capabilities that "phone home", keyloggers, rootkits, and web beacons.Spyware is mostly used for the purposes of tracking and storing Internet users' movements on the Web and serving up pop-up ads to Internet users. Whenever spyware is used for malicious purposes, its presence is typically hidden from the user and can be difficult to detect. Some spyware, such as keyloggers, may be installed by the owner of a shared, corporate, or public computer intentionally in order to monitor users

 small infectious agent that replicates only inside the living cells of other organisms. Viruses can infect all types of life forms, from animals and plants to microorganisms, including bacteria and archaea. Since Dmitri Ivanovsky's 1892 article describing a non-bacterial pathogen infecting tobacco plants, and the discovery of the tobacco mosaic virus by Martinus Beijerinck in 1898,about 5,000 virus species have been described in detail, although there are millions of types. Viruses are found in almost every ecosystem on Earth 

Spam or SPAM may refer to:

• Spamming, unsolicited or undesired electronic messages

• Email spam, unsolicited, undesired, or illegal email messages

• Messaging spam, spam targeting users of instant messaging (IM) services, sms or private messages within websites