Korea Hydro & Nuclear Power Co., the sole operator of South Korea's nuclear power plants, said Sunday that it has separated its internal computer network from the Internet in an effort to guard against possible cyber attacks.
   
The state-run company said it has also completely divided its nuclear plant control systems from its internal computer networks and restricted both systems' access to the Internet.

USB ports of the nuclear power plant control systems have also been sealed, it added.    

The network separation is the safest way of protecting the nuclear power plants from hacking attacks from the outside, the company explained.
   
South Korea has 23 reactors nationwide, which generate around 35 percent of the country's electricity.   

Last week, South Korea's government announced that North Korea was behind the massive hacking attack that paralyzed the networks of local financial firms and broadcasters last month, though the North later denied its involvement.   

Three South Korean banks -- Shinhan, NongHyup and Jeju -- and their insurance affiliates as well as three TV broadcasters -- KBS, MBC and YTN -- were hit by the cyber attack as malicious code infected some 48,000 computers in their networks on March 20.   

North Korea is known to operate a cyber warfare unit of 3,000 elite hackers who are trained to break into computer networks to steal information and distribute malware.
   
In addition to the hacking attacks, the North has been interfering with global positioning system signals since 2010, disrupting hundreds of South Korean commercial ships and flights in the border area. (Yonhap News)