epa04537814 (FILE) A file picture dated 22 March 2013 shows two reactors of the nuclear power plant in Wolseong, South Korea. South Korea’s nuclear power operator began cyber attack drills defending its plants against simulated hacks, an official said 22 December 2014, after technical details of the plants were revealed online. The tests would be carried out over two days on four of the country’s 23 nuclear power sites, an official of the Korea Hydro and Nuclear Power Company said. A hacker this month posted designs and manuals for two facilities on Twitter, Yonhap News Agency reported, and threatened to publish more secrets if the authorities do not shut down the reactors on Christmas day. The operator reiterated that the leaks are not related to core techologies and do not undermine the reactors’ safety or security. EPA/UDO WEITZ *** Local Caption *** 50849726