1. A system, residing on a computer system that is connected to the Internet and has a processor, a storage, and communication platform, for retrieving advertisement information with respect to an Internet search request, comprising: a log system, operative via the processor of the computer system, configured for processing a log recording users' visits in a first database accessible to the computer system; an indexing system, operative via the processor of the computer system, configured for obtaining index data, in a second database accessible from the computer system where the indexing system resides, based on the log or processing result thereof; and a retrieval system, operative via the processor of the computer system, configured for identifying one or more advertisements, from a third database storing advertisements, with respect to a search request received from a user, wherein the index data related to the user are established based on the user's past visits, and the one or more advertisements are identified based on the index data related to the user so that the one or more advertisements are selected to match the user's past search behavior characterized at least partially by the log.