Before filing a spam report with the search engines, please read What is search spam, or SEO spam? to learn how to spot search spam in the search results. Filing a Google Spam Report
Reporting spam in the Google results is easy. Just visit Google - Report a Spam Report, fill out the form, and click the "submit" button at the bottom of the page. Filing a Yahoo! Spam Report
As Yahoo! has aquired several major search engines recently, your Yahoo! spam report goes further than it did in the past. Now, filing a Yahoo! spam report will also affect Alltheweb.com and others. Just visit Yahoo! > Search Help > Search Spam Report, fill out the form, and click the "send" button at the bottom of the page.
