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E-mail spam, also known as junk e-mail, is a subset of spam that involves nearly identical messages sent to numerous recipients by e-mail. A common synonym for spam is unsolicited bulk e-mail (UBE). Definitions of spam usually include the aspects that email is unsolicited and sent in bulk.^{[1][2][3][4][5]} "UCE" refers specifically to unsolicited commercial e-mail.

E-mail spam has steadily, even exponentially grown since the early 1990s to several billion messages a day. Spam has frustrated, confused, and annoyed e-mail users. Laws against spam have been sporadically implemented, with some being opt-out and others requiring opt in e-mail. The total volume of spam (over 100 billion emails per day as of April 2008^[update]) has leveled off slightly in recent years, and is no longer growing exponentially. The amount received by most e-mail users has decreased, mostly because of better filtering. About 80% of all spam is sent by fewer than 200 spammers. Botnets, networks of virus-infected computers, are used to send about 80% of spam. Since the cost of the spam is borne mostly by the recipient,^[6] it is effectively postage due advertising.

E-mail addresses are collected from chatrooms, websites, newsgroups, and viruses which harvest users' address books, and are sold to other spammers. Much of spam is sent to invalid e-mail addresses. ISPs have attempted to recover the cost of spam through lawsuits against spammers, although they have been mostly unsuccessful in collecting damages despite winning in court.^[7][8] Spam averages 94% of all e-mail sent.^[9]

Overview

From the beginning of the Internet (the ARPANET), sending of junk e-mail has been prohibited,^[10] enforced by the Terms of Service/Acceptable Use Policy (ToS/AUP) of internet service providers (ISPs) and peer pressure. Even with a thousand users junk e-mail for advertising is not tenable, and with a million users it is not only impractical,^[11] but also expensive.^[12] It is estimated that spam cost businesses on the order of $100 billion in 2007.^[13] As the scale of the spam problem has grown, ISPs and the public have turned to government for relief from spam, which has failed to materialize.^[14]

[edit] Types

Spam has several definitions, varying by the source.

• Unsolicited bulk e-mail (UBE)—unsolicited e-mail, sent in large quantities.
• Unsolicited commercial e-mail (UCE)—this more restrictive definition is used by regulators whose mandate is to regulate commerce, such as the U.S. Federal Trade Commission.

[edit] Spamvertised sites

Many spam e-mails contain URLs to a website or websites. According to a Commtouch report in June 2004, "only five countries are hosting 99.68% of the global spammer websites", of which the foremost is China, hosting 73.58% of all web sites referred to within spam.^[15]

[edit] Most common products advertised

According to information compiled by Spam-Filter-Review.com, E-mail spam for 2006 can be broken down as follows.^[16]

Rolex watches and Viagra-type drugs are two common products advertised in spam e-mail.^[17][18]

[edit] 419 scams

Advance fee fraud spam such as the Nigerian "419" scam may be sent by a single individual from a cyber cafe in a developing country. Organized "spam gangs" operating from Russia or eastern Europe share many features in common with other forms of organized crime, including turf battles and revenge killings.^[19]

[edit] Phishing

Spam is also a medium for fraudsters to scam users to enter personal information on fake Web sites using e-mail forged to look like it is from a bank or other organization such as PayPal. This is known as phishing. Spear-phishing is targeted phishing, using known information about the recipient, such as making it look like it comes from their employer.^[20]

[edit] Appending

If a marketer has one database containing names, addresses, and telephone numbers of prospective customers, they can pay to have their database matched against an external database containing email addresses. The company then has the means to send email to persons who have not requested email, which may include persons who have deliberately withheld their email address. ^[21]

[edit] Image spam

Image spam is an obfuscating method in which the text of the message is stored as a GIF or JPEG image and displayed in the email. This prevents text based spam filters from detecting and blocking spam messages. Image spam is currently used largely to advertise "pump and dump" stocks.^[22]