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Spamming is the abuse of electronic messaging systems to
indiscriminately send unsolicited bulk messages. While the most widely
recognized form of spam is e-mail 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, mobile phone messaging spam, Internet forum spam and junk fax transmissions.

Spamming remains economically viable because advertisers have no
operating costs beyond the management of their mailing lists, and it is
difficult to hold senders accountable for their mass mailings. Because
the barrier to entry
is so low, spammers are numerous, and the volume of unsolicited mail
has become very high. The costs, such as lost productivity and fraud,
are borne by the public and by Internet service providers,
which have been forced to add extra capacity to cope with the deluge.
Spamming is widely reviled, and has been the subject of legislation in
many jurisdictions.[citation needed]

Persons who create electronic spam are called spammers.[1]

E-mail spam, also known as unsolicited bulk email (UBE) or
unsolicited commercial email (UCE), is the practice of sending unwanted
e-mail messages, frequently with commercial content, in large
quantities to an indiscriminate set of recipients.

Spam in e-mail started to become a problem when the Internet was
opened up to the general public in the mid-1990s. It grew exponentially
over the following years, and today comprises some 80 to 85% of all the
email in the world, by conservative estimate;[2] some sources go as high as 95%.

Pressure to make e-mail spam illegal has been successful in some
jurisdictions, but less so in others. Spammers take advantage of this
fact, and frequently outsource parts of their operations to countries
where spamming will not get them into legal trouble.

Increasingly, e-mail spam today is sent via "zombie networks", networks of virus- or worm-infected personal computers in homes and offices around the globe; many modern worms install a backdoor which allows the spammer access to the computer. At the same time, it is becoming clear that malware authors, spammers, and phishers are learning from each other, and possibly forming various kinds of partnerships.

E-mail is an extremely cheap mass medium, and professional spammers
have automated their processes to a high extent. Thus, spamming can be
very profitable even at what would otherwise be considered extremely
low response rates.

An industry of e-mail address harvesting is dedicated to collecting email addresses and selling compiled databases.[3] Millions of email addresses can be cheaply purchased.[4]