Spam is the abuse of electronic messaging systems to send unsolicited bulk messages indiscriminately. 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, Online classified ads spam, mobile phone messaging spam, Internet forum spam, junk fax transmissions, and file sharing network spam.
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.
People who create electronic spam are called spammers.
Spamming in different media
E-mail spam
E-mail spam, known as unsolicited bulk Email (UBE), junk mail, 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; 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 and use it for malicious purposes. This complicates attempts to control the spread of spam, as in many cases the spam doesn't even originate from the spammer. In November 2008 an ISP, McColo, which was providing service to botnet operators, was depeered and spam dropped 50%-75% Internet-wide. 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.
An industry of e-mail address harvesting is dedicated to collecting email addresses and selling compiled databases. Some of these address harvesting approaches rely on users not reading the fine print of agreements, resulting in them agreeing to send messages indiscriminately to their contacts. This is a common approach in social networking spam such as that generated by the social networking site Quechup.
Instant Messaging Spam
Instant Messaging spam, sometimes termed spim (a portmanteau of spam and IM, short for instant messaging), makes use of instant messaging systems. Many IM systems offer a user directory, including demographic information that allows an advertiser to gather the information, sign on to the system, and send unsolicited messages. To send instant messages to millions of users requires scriptable software and the recipients' IM user names. Spammers have similarly targeted Internet Relay Chat channels, using IRC bots that join channels and bombard them with advertising.
