Each search engine has strengths and weaknesses and one search engine may have indexed Web sites that another has not. Metasearch engines have been developed to overcome this problem. When presented with a search query they submit it to a variety of engines and display the combined results. Three of the most famous meta searchengines are Savvysearch, dogpile, and MetaCrawler. Many of these search engines now allow the option of nominating which combination of search engine to use for a particular search. Metasearch engines were very controversial when they were first developed as they did not retrieve the banner advertising that individual search engine developers used to raise revenue.