SEOUL - A fresh wave of cyber attacks hit major South Korean Web sites, including that of the presidential office Cheong Wa Dae, on Friday, local media reported, citing industrial sources.

Starting 10 am Friday, 40 web sites, including the ones of presidential office Cheong Wa Dae, the Ministry of Foreign Affairs and Trade and top lender Kookmin Bank, came under distributed denial-of-service (DDoS) attacks, Yonhap News Agency reported, citing AhnLab, South Korea's top information security company.

Additional attacks are expected to come at 6:30 pm, Yonhap said.

DDoS attacks are unsophisticated but pose great difficulties for websites to defend against. The attacker directs a giant traffic surge to its target, overwhelming the site's servers and making it hard for legitimate users to access the site.