The U.S. National Security Agency, which has a cybersecurity mission in addition to surveillance, has disputed a report that it knew about the Heartbleed security vulnerability for at least two years before other researchers disclosed the flaw this month. The NSA used Heartbleed to gather intelligence, according to a report from Bloomberg, quoting two anonymous sources. Heartbleed is a flaw in OpenSSL that could allow attackers to monitor all information passed between a user and a Web service.