A method and system for sharing search index entries across multiple computer systems organized in a peer to peer network, in which unique content is indexed only once, even though the content may be physically duplicated in multiple computer systems in the peer to peer network. When files are obtained by a shared indexing service, and a determination is made as to whether the received files are duplicates with regard to previously indexed files. If a file is determined to be a duplicate, the index representation of the previously indexed copy of the file is modified to indicate that the file is also associated with another computer system in the peer to peer network. If a file is not a duplicate of a previously indexed file, the file is indexed to support future searches. The index representation of a file includes category identifiers associating one or more computer systems with the file. When a file is indexed, one or more category identifiers are generated and stored in association with that file. The category identifiers for an indexed file may represent host computer systems on which copies of the file are stored. The category identifiers enable location specific searching by computer systems in a peer to peer network sharing a common search index. A software category filter may be provided to process search results from the shared search index, so that only files associated with certain categories are returned.