Phishing is the attempt to obtain sensitive information such as usernames, passwords, and credit card details (and, indirectly, money), often for malicious reasons, by disguising as a trustworthy entity in an electronic communication.

The word is a neologism created as a homophone of fishing due to the similarity of using a bait in an attempt to catch a victim.

According to the 3rd Microsoft Computing Safer Index Report released in February 2014, the annual worldwide impact of phishing could be as high as $5 billion.

Email filtering is the processing of email to organize it according to specified criteria.

Most often this refers to the automatic processing of incoming messages, but the term also applies to the intervention of human intelligence in addition to anti-spam techniques, and to outgoing emails as well as those being received.

Malware, short for malicious software, is any software used to disrupt computer or mobile operations, gather sensitive information, gain access to private computer systems, or display unwanted advertising.

Before the term malware was coined by Yisrael Radai in 1990, malicious software was referred to as computer viruses.

The first category of malware propagation concerns parasitic software fragments that attach themselves to some existing executable content.

The fragment may be machine code that infects some existing application, utility, or system program, or even the code used to boot a computer system.

Malware is defined by its malicious intent, acting against the requirements of the computer user, and does not include software that causes unintentional harm due to some deficiency.

Electronic spamming is the use of electronic messaging systems to send an unsolicited message (spam), especially advertising, as well as sending messages repeatedly on the same site.

While the most widely recognized form of spam is email spam, the term is applied to similar abuses in other media: instant messaging spam, Usenet newsgroup spam, Web search engine spam, spam in blogs, wiki spam, online classified ads spam, mobile phone messaging spam, Internet forum spam, junk fax transmissions, social spam, spam mobile apps, television advertising and file sharing spam.

It is named after Spam, a luncheon meat, by way of a Monty Python sketch about a menu that includes Spam in every dish.

The food is stereotypically disliked/unwanted, so the word came to be transferred by analogy.

A computer virus is a type of malicious software program ("malware") that, when executed, replicates by reproducing itself (copying its own source code) or infecting other computer programs by modifying them.

Infecting computer programs can include as well, data files, or the "boot" sector of the hard drive.

When this replication succeeds, the affected areas are then said to be "infected" with a computer virus.

The term "virus" is also commonly, but erroneously, used to refer to other types of malware.

"Malware" encompasses computer viruses along with many other forms of malicious software, such as computer "worms", ransomware, trojan horses, keyloggers, rootkits, spyware, adware, malicious Browser Helper Object (BHOs) and other malicious software.

The majority of active malware threats are actually trojan horse programs or computer worms rather than computer viruses.

The term computer virus, coined by Fred Cohen in 1985, is a misnomer.

Viruses often perform some type of harmful activity on infected host computers, such as acquisition of hard disk space or central processing unit (CPU) time, accessing private information (e.g., credit card numbers), corrupting data, displaying political or humorous messages on the user's screen, spamming their e-mail contacts, logging their keystrokes, or even rendering the computer useless.

However, not all viruses carry a destructive "payload" and attempt to hide themselves—the defining characteristic of viruses is that they are self-replicating computer programs which install themselves without user consent.