1. A computer-implemented method of determining privacy-safe queries for providing to an advertiser, the method comprising: receiving a request from the advertiser for query statistics for an ad provided by the advertiser; identifying a first set of search queries from a search query log that includes search queries submitted to a search service over a predetermined length of time, wherein the search query log indicates that each query in the first set of search queries triggered at least one display of the ad that resulted in a user clicking on the ad; identifying a second set of search queries from the first set of search queries, the identifying including selecting search queries from the first set of search queries and for each selected search query: determining a number of unique identifiers associated with the selected search query, each unique identifier being associated with a unique client device that submitted a search request containing the search query; in response to determining that the number of unique identifiers exceeds a predetermined number of unique identifiers, including the selected search query in the second set of search queries, wherein the predetermined number of unique identifiers has a value greater than one and results in each search query included in the second set of search queries being specified as privacy-safe, and wherein each search query included in the second set of search queries does not include personal information; and providing the second set of search queries and query statistics for each query in the second set of search queries to the advertiser in response to the request.