“Web spam” constitutes a serious threat to the integrity of search results from some search engines; it is also known as “spamdexing”, “search spam” and “search engine spam”. By including many terms that are popular as keywords — but may not bear any relationship to the contents of a web site — and other techniques, search engine optimizers hope to promote their web site to a prime position in the rankings of search results. This obscures and contaminates the results with many irrelevant sites. The development in the 1990s of “link farms ” or “content farms” constitutes a further threat: these consist of little material but many links to each other in an attempt to fool search engine algorithms into rating such sites highly because of link density. Some search engine companies have recognised the dangers and implemented specific checks for “web spam” and the filtering-out of offending sites. A recently-developed search engine, Blekko (http://blekko.com/), which was launched on 1 November 2010, is adopting a strict policy of suppressing results from some twenty “link farms” to ensure that its search results are uncontaminated. Blekko also uses human intervention to locate reputable sites and improve the precision of a search. The idea of “slashtags” is a key development by Blekko: these are simple words such as “/science” or “/sports” that can be added to the end of a search query to offer improved results for that topic. The slashtags can be subject areas but may also represent matters of opinion; so, adding /reviews allows a particular slant on a search focussing on the arts. Blekko will also add slashtags automatically when it becomes evident that you wish to focus on an aspect of a particular topic. The company has also launched the “Spam Clock” (http://www.spamclock.com/) as an indication (non-scientific, they stress) of the volume of web spam that threatens good searching.