Link spam is the posting of out-of-context links on websites, discussion forums, blog comments, guestbooks or any other online venue that displays user comments. Link spam is also known as comment spam, blog spam or wikispam. Link spammers usually don’t leave comments of any value along with their links.
The purpose of link spam is to increase the number of external links made to a site the spammer wishes to promote. A greater number of links made to a page, among other things, increases a page’s rank and improves its position on search engine results pages (SERP). Higher rankings in web searches mean greater visibility over competitors, more visitors and potentially more paying customers.
Link spam started in website guestbooks, where the spammer would repeatedly paste links to the site they were promoting. Around 2003, spammers began to attack open comments in blogs. Currently, many blog software systems have ways of eliminating or minimizing link spam. For example, Jay Allan created MT-BlackList, a free plugin to combat link spam on Movable Type-based blogs.
Because common targets were being protected, spammers began looking elsewhere, such as wikis. As a result, wikispam was born. Many wikis, including Wikipedia, have pages in their sandbox testing areas filled with spammed links, along with active pages that are defaced by links.
Link spamming can backfire on the perpetrator when search engines decide a site is a bad neighbor and remove it from search results altogether. Measures to prevent or reduce comment spam include requiring manual approval of comments containing and using a blacklist of banned words to detect spam.