South Korea's government computer systems have not been affected by the crippling ransomware WannaCry, which hit hundreds of thousands of computers around the world last week, a government official said Monday.

"We've taken necessary measures against WannaCry, and no damage has been reported as of Monday morning," the official at the Interior Ministry's integrated government computer center said.

The ransomware encrypts victims' files in a computer until they pay for decrypting them. The WannaCry onslaught, first detected Friday and the biggest ever of its kind, is known to have infected some 200,000 computers in 150 countries around the world thus far.

"All business computers of local governments are also safe from the attack as they are linked to the ministry's computer center," the official said, adding that the center completed security patch updates, especially for servers and PCs that use MS Windows.

In the meantime, South Korea's major theater chain CJ CGV said around 50 of its complexes are estimated to have been attacked by the malware.

The presidential office said the government has issued a preliminary warning against the ransomware.

"The National Intelligence Service raised its alert level for cybersecurity from normal to caution as of 6 p.m. Sunday," chief presidential press secretary Yoon Young-chan told a press briefing.

"The government has also taken additional security measures at public institutions, which include reinforcing their firewalls," he added. (Yonhap)