The Web sites of South Korea's presidential office, government agencies and financial institutions came under a cyber attack on Friday, industry sources said.

The presidential office Cheong Wa Dae, the Ministry of Foreign Affairs and Trade and top lender Kookmin Bank were among some 40 institutions whose Web sites were infected by the so-called distributed denial-of-service (DDoS) from 10 a.m., AhnLab Inc. said in a statement.

Additional attacks were expected to begin at 6:30 p.m., said AhnLab, South Korea's top information security company.

The latest DDoS attack, which was launched by malicious codes that turn personal computers into zombie PCs, bears resemblance to the cyber attack that targeted 17 local Web sites in July 2009, it added. (Yonhap)