A spambot is a computer program designed to assist in the sending of spam. Spambots usually create accounts and send spam messages with them. Web hosts and website operators have responded by banning spammers, leading to an ongoing struggle between them and spammers in which spammers find new ways to evade the bans and anti-spam programs, and hosts counteract these methods.
The simplest method involves spammers purchasing or trading lists of email addresses from other spammers. Another common method is the use of special software known as "harvesting bots" or "harvesters", which spider Web pages, postings on Usenet, mailing list archives, internet forums and other online sources to obtain email addresses from public data. Spammers may also use a form of dictionary attack in order to harvest email addresses, known as a directory harvest attack, where valid email addresses at a specific domain are found by guessing email address using common usernames in email addresses at that domain. For example, trying alan@example.com, alana@example.com, alanb@example.com, etc. and any that are accepted for delivery by the recipient email server, instead of rejected, are added to the list of theoretically valid email addresses for that domain. Another method of email address harvesting is to offer a product or service free of charge as long as the user provides a valid email address, and then use the addresses collected from users as spam targets. Common products and services offered are jokes of the day, daily bible quotes, news or stock alerts, free merchandise, or even registered sex offender alerts for one's area. Another technique was used in late 2007 by the company iDate, which used email harvesting directed at subscribers to the Quechup website to spam the victim's friends and contacts. 1621373253@na6.eu
Source: Wikipedia