Technology giants in the US have written an open letter to President Obama urging him to make tighter controls on surveillance. <br /><br />The spying scandal involving the US National Security Agency was revealed after documents were leaked by the whistleblower Edward Snowden.<br /><br />The firms are worried public suspicion could affect their profits.<br /><br />Al Jazeera's Shihab Rittansi reports from Washington.
