Seoul, Jan 28 : Twelve South Korean websites attacked by a Chinese hacking group remain unable to be accessed five days after the incident, industry sources said. The Chinese attackers, identifying themselves as Xiaoqiying, hacked into the websites of 12 academic organizations and institutions Sunday, including the Korea Research Institute for Construction Policy, the Korean Archaeological Society and the Korean Academy of Basic Medicine & Health Science. The attack took place in the middle of the four-day Lunar New Year holiday that began last Saturday, reports Yonhap news agency. According to the Korean internet safety watchdog, the hackers used the SQL injection technique to exploit a security vulnerability in the websites' software and corrupt the database contents. After the breach, most of the attacked websites showed an error page or a warning message by the hacking group. "We are working on determining the exact cause of the case and restoring the damage, but it takes some time," said an official from the cybersecurity authorities, asking for anonymity. The South Korean government is now looking into some 40 files disclosed by the Chinese hacking group Thursday. The group claimed it had stolen the data from South Korea's government and public institutions. It also said it had successfully compromised the computer networks of 70 South Korean educational institutions around the Lunar New Year holiday that ran from Saturday to Tuesday. /IANS