WASHINGTON (Reuters) - The Internal Revenue Service is investigating whether unauthorized people gained access to sensitive taxpayer and bank account information but has not yet exposed any privacy breaches, an official said on Friday. The U.S. tax agency -- whose databases include suspicious activity reports from banks about possible terrorist or criminal transactions -- launched the probe after the Government Accountability Office said in April that the IRS "routinely permitted excessive access" to the computer files. The GAO team was able to tap into the data without authorization, and gleaned information such as bank account holders' names, social security numbers,...