Seoul , South Korea ( CNN ) -- A cyber attack Friday morning hit 40 South Korean websites , including those of several government agencies and major banks , the country 's internet security agency said . The government detected the first wave of the attack Thursday . It was coordinated from outside South Korea using `` zombie '' computers -- computers which have downloaded malicious codes -- to target designated websites , slow them down or paralyze their operation , the internet security agency said . Infected computers directed a giant traffic surge to targeted websites . That 's called a DDoS attack , short for distributed denial-of-service -- and it 's hard for most sites to defend against . By Friday , South Korea 's leading security software company had developed a free anti-virus program to treat infected computers . Software company AhnLab said it developed the anti-virus program after receiving reports of the attack from the South Korean government Thursday . The company warned that another attack would hit websites at 6:30 p.m. Friday . Targeted sites include South Korea 's presidential office , the foreign ministry , the defense ministry and main banking websites , according to a statement issued by AhnLab . No severe damage has been reported so far , but the government said it was monitoring the attack . During a similar attack in 2009 , 17 South Korean websites were hit over a three-day period .
Officials say the attack is being coordinated from outside South Korea . Infected ` ` zombie '' vehicles are directing traffic surges to certain targets . These include South Korea 's presidential office , foreign ministry and defense ministry . Other South Korean sites were hit during a similar attack over three days in October .