Used by Search engines algorithms, whose purpose is to cleanse search results from poor-quality, spam, useless, unique web pages, as well as sites that are caught in dishonest manipulation of positions using methods "black", and sometimes "gray" SEO.

The most “unpleasant” are search engine filters that use pessimization (lower positions) and sending sites to ban (temporary or permanent exclusion from index). These are:

- AGC, "You are the last", You are spamny" at Yandex;

- "Panda"and"Penguin»y Google.

Getting out of such filters is quite difficult because of the undermined search engine's confidence in it. Sometimes it’s much easier to create a new resource than to save an existing one to which “heavy” were applied sanctions.