"Hundreds of thousands" of Chinese computers at nearly 30,000 institutions including government agencies have been hit by the global ransomware attack, a leading Chinese security-software provider has said, though the Asian impact has otherwise been relatively muted.
The enterprise-security division of Qihoo 360, one of the country's leading suppliers of anti-virus software, said 29,372 institutions ranging from government offices to universities, ATMs and hospitals had been "infected" by the outbreak as of late Saturday.
Governments, companies and computer experts around the world braced on Monday for a possible worsening of the global cyberattack that has hit more than 150 countries as people return for another work week.
The indiscriminate attack began Friday and struck banks, hospitals and government agencies, exploiting known vulnerabilities in older Microsoft computer operating systems.
In a statement dated Sunday, Qihoo 360 said the ransomware had spread particularly quickly through higher education, affecting more than 4,000 Chinese universities and research institutions.
It gave few details on the extent of any damage, however, and China's government has said little about the situation.
Chinese state media on Monday quoted national cyberspace authorities as saying the attack is still spreading in the country, but had slowed significantly.
State-owned oil giant PetroChina said in a statement that it had to disconnect the networks linking its petrol stations nationwide for 12 hours on Saturday after the company's internet payment functions were disabled.
Customers were forced to use cash during the shutdown. By late Sunday, around 80 percent of its network was back online, PetroChina said.
In Japan, a spokesman for conglomerate Hitachi said on Monday that the company's computer networks were "unstable", crippling its email systems.
"We found the problems this morning. We assume that the problems are due to the weekend's global cyberattacks. We have not received any reports of damage to our production. We don't know when the problem can be solved," said the spokesman, who spoke on condition of anonymity.
Authorities across the world have issued public alerts warning computer users to beware of suspicious emails and beef up their computer security measures.
"Please beware and take preventive steps against the malware attack," said Indonesia's information minister Rudiantara who, like many Indonesians, goes by one name.
Rudiantara was speaking to reporters following reports that records and billing systems in at least one hospital in the country had been crippled.
Dozens of Chinese universities have issued alerts about the attack and advised students to disable their internet connections before turning on their computers.
The southern city of Zhuhai on Monday suspended all activities in its housing pension system, which mainly offers loans to homebuyers, while it protectively upgraded its internet security, according to a statement by the city's Housing Provident Fund Management Center.
The attack sent the stock prices of Chinese internet security firms soaring in the Shenzhen market.