10. An apparatus for determining privacy-safe queries for providing to an advertiser, the apparatus comprising: a query statistics engine to automatically identify first and second sets of search queries that have a low probability of including personal data of users who submitted the search queries, in which the query statistics engine identifies the 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, and where the query statistics engine determines that the search query log indicates that each query in the first set of search queries triggered at least one display of an ad that resulted in a user clicking on the ad, and where the query statistics engine selects search queries from the first set of search queries and for each selected search query: determines 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, includes 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 a data storage device to store the second set of search queries in association with the ad.
10. An apparatus for determining privacy-safe queries for providing to an advertiser, the apparatus comprising: a query statistics engine to automatically identify first and second sets of search queries that have a low probability of including personal data of users who submitted the search queries, in which the query statistics engine identifies the 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, and where the query statistics engine determines that the search query log indicates that each query in the first set of search queries triggered at least one display of an ad that resulted in a user clicking on the ad, and where the query statistics engine selects search queries from the first set of search queries and for each selected search query: determines 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, includes 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 a data storage device to store the second set of search queries in association with the ad. 11. The apparatus of claim 10 , further comprising a search server to receive search requests containing search queries, and store the search queries in the data storage device.