Siri uses Bing and Wolfram Alpha for Web searches, but it might want to index the Web if it's building a search engine to support mobile apps. Some think Apple is building its own search engine, but the company has never seen that as a priority. They focus more on the hardware. Rumors began last fall, when webmasters began seeing Web crawler visits from IP addresses starting with 17 -- the IP address block owned entirely by Apple. Ben Lovejoy explains.