Search engines make screening of sites, not allowing some of them to occupy high positions on requests. This is accomplished through special filters in order only the most qualitative resources were on the top of the SERP. Every search engine has its own set of filters, by which your site is checked on compliance with certain criteria.
Google has following filters:
Google Florida – prevents excessive internal optimization. Applied to the pages, which are supersaturated with keywords and to the pages on which is often used the highlight of words with italics or bold font. From time to time the filter is changed, now its reaction to the actions of optimizers is less rigid than it was in the beginning. If the pages became subject to Florida, then you need to remove some of the elements of optimization.
Google Sandbox acts on the new sites. 2-3 months young site is in a "sandbox" and it will stay there, until it will deserve the trust of search engines. At this stage, site needs high-quality content and regular updates.
Too many pages at once Filter. You can also get a filter for excess of information. Or rather for its sharp infusion. A large number of pages, that appear in a short time may look like automatic content filling, which relates to unfair methods of search engine promotion. So its best to regularly update the content of your site in small portions.
Google Supplemental Results – under its scope fall pages, that contain material resembling to other pages of your resource. And they will not get to the SERP, while there will be enough information in the main search results.
Broken Link Filter – works if the site has many links to non-existent page. You can check your site for broken links using special programs.
Page Load Time Filter - is superimposed to sites which needs long time to load.
Google Duplicate Content – is applied for content duplication. If the filter is imposed, all the promotional methods become useless. The recipe is simple - content must be unique.
Google Panda – new integrated filter from Google, which carries about 100 parameters. Increases the relevance of a page in search results.
Mentioned above filters are applied in the case of improper internal optimization. Further Google filters, are associated with external factors.
Google – 30 - is applies when using (or suspected to be used) prohibited ways of promotion. After laying of the filter positions in the SERP are reduced by 30 places, and if violations are not corrected, then site may be completely excluded from the index. In this case, to resume indexing after the exclusion of black methods, you need to contact Google tech support.
Google Bombing – a large number of inbound links with identical anchor text leads to application of this filter. May you will need to remove a certain part of them and buy new ones. Its also desirable to have some number of 'natural' anchors.
Co-Citation Filter – for external links from the sites of prohibited topics.
Before purchasing you need to carefully check the donor links.
To Many Links at Once Filter – for the sharp increase in the number of external links. Young sites should not add more than seven links per day.
Without knowledge of the major sanctions you can easily bring your site under the action of filters, even without using of "black" methods of promotion.