An anti-spam tool works with a web browser to detect spam webpages locally on a client machine. The anti-spam tool can be implemented either as a plug-in module or an integral part of the browser, and manifested as a toolbar. The tool can perform an anti-spam action whenever a webpage is accessed through the browser, and does not require direct involvement of a search engine. A spam detection module installed on the computing device determines whether a webpage being accessed or whether a link contained in the webpage being accessed is spam, by comparing the URL of the webpage or the link with a spam list. The spam list can be downloaded from a remote search engine server, stored locally and updated from time to time. A two-level indexing technique is also introduced to improve the efficiency of the anti-spam tool's use of the spam list.