SEOUL, South Korea (CNN) -- The suspected cyberattack targeting South Korean banks and broadcasters originated from an IP address in China, South Korean regulators said Thursday, heightening suspicions of North Korean involvement.
The attack Wednesday damaged 32,000 computers and servers at media and financial companies, South Korea's Communications Commission said.
It infected banks' and broadcasters' computer networks with a malicious program, or malware, that slowed or shut down systems, officials and the semiofficial Yonhap News Agency said.
Suspicion immediately fell on North Korea, which has recently renewed threats to go to war with the South amid rising tensions over Pyongyang's nuclear weapons, and missile testing and international efforts to stop them.
Some past cyberattacks on South Korean organizations that officials linked to North Korea were traced to IP addresses in China. An IP address is the number that identifies a network or device on the Internet.
South Korean officials are still analyzing the cause of the network crashes and are working to prevent any further damage, the communications commission said.
The military has stepped up its cyberdefense efforts in response to the widespread outages, which hit nine companies, Yonhap reported, citing the National Police Agency.
Government computer networks did not seem to be affected, Yonhap cited the National Computing and Information Agency as saying.
A joint team from government, the military and private industry was responding.
A South Korean official close to the investigation told CNN that malicious computer code spread through hacking caused the outages.
How the hackers got in and spread the code remains under investigation, and analysts are examining the malware, the official said.
South Korean officials have not said who they suspect unleashed the malicious code, but experts believe it is consistent with what North Korea has done in the past.
"It's happened before in similar circumstances where there have been tensions on the peninsula," said Adam Segal, a cybersecurity expert with the Council on Foreign Relations.
There didn't appear to be any mention of the computer crash in North Korean state media.
South Korea has accused the North of similar hacking attacks before, including incidents in 2010 and 2012 that also targeted banks and media organizations. The North rejected the allegations.
The outages come amid heightened tensions on the Korean Peninsula, with the North angrily responding to a recent U.N. Security Council vote to impose tougher sanctions on Pyongyang after the country's latest nuclear test last month.
Last week, North Korea invalidated its 60-year-old armistice with the South. It has threatened to attack its neighbor with nuclear weapons and has also threatened the United States.
The armistice agreement, signed in 1953, ended the three-year war between North and South but left the two nations technically in a state of war.
The United States has deployed B-52 bombers to conduct high-profile flyovers of its South Korean ally and announced that it will deploy new ground-based missile interceptors on its West Coast against the remote possibility that North Korea could strike the United States with long-range weapons.
Last week, North Korea complained that it was the victim of "intensive and persistent virus attacks" from the United States and South Korea, according to KCNA, the official North Korean news agency.
Yonhap said Wednesday's outages affected three broadcasters, four banks and two insurance companies.
The three broadcasters -- KBS, MBC and YTN -- reported varying levels of trouble containing the virus. While the networks remained on the air, cable network YTN said editing equipment had been affected and it expected to experience broadcasting problems, Yonhap reported.
Computer networks stopped working entirely at three banks -- Shinhan, Nonghyup and Jeju -- around 2 p.m. Wednesday, Yonhap reported, citing the National Police Agency. Another financial institution, Woori Bank in Seoul, reported it was able to fend off a hacking attack about the same time.
The banks that were affected reported problems with a variety of systems, including Internet banking, ATMs and telecommunication services, and some branches stayed open late because of the slowdown, Yonhap said.
-- CNN's K.J. Kwon reported from Seoul, Jethro Mullen from Hong Kong and Michael Pearson from Atlanta. Judy Kwon in Hong Kong contributed to this report.
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