SEOUL, South Korea (CNN) -- South Korean police said Wednesday they are investigating a widespread computer outage that has struck systems at leading television broadcasters and banks, prompting the military to step up its cyberalert level amid concerns about North Korea.
The South Korean communications regulator reportedly linked the computer failures to hacking that used malicious code, or malware.
Networks at the different companies began to encounter difficulties starting around 2 p.m. local time (1 a.m. ET).
One television station, YTN, reported that 500 of its computers had been disabled by the outage after staff members received a message on their computers asking them to reboot.
Another, KBS, said that its internal networks had been "paralyzed," but the problem didn't prevent it from broadcasting live. A third broadcaster, MBC, was also reportedly experiencing problems.
Meanwhile, Shinhan Bank, a large lender, said its system was paralyzed for more than an hour and a half before it was able to get it back to operating normally.
A second lender, Nonghyup Bank, said that it had disconnected some of its computers after they were infected with a virus. The bank said its main server was still functioning and able to carry out Internet transactions.
And Jeju Bank said it had had problems with some computers and ATMs, most of which it had resolved by late afternoon.
Police didn't immediately provide an explanation for the computer difficulties experienced by the six companies.
But the Korea Communications Commission, a regulatory body, said the cause of the network failures appeared to be hacking attacks that used malware, the semiofficial news agency Yonhap reported.
The South Korean Defense Ministry said it had upgraded its information operations condition, or INFOCON, one notch to level 3 in response to the outages. Level 1 is the highest on the five-notch scale, which gauges the perceived likelihood of a network attack.
The ministry said it couldn't say whether North Korea, which has made recent threats against South Korea and the United States, was behind the computer problems.
It said it had already increased the alert level one notch last month in response to the North Korean threats.
The South Korean government has set up a cyber crisis management team, bringing together civilian, government and military officials, said Kim Haing, a spokeswoman for the South Korean president's office.
South Korea has experienced multiple cyberattacks on government, business and military websites in recent years.
Seoul has previously pinned blame on North Korea for some of the attacks, a claim that Pyongyang has denied.
Concerns remain high about Internet security in the South, one of the most wired countries in the world, and experts have pointed out vulnerabilities.
Last year, Gen. James Thurman, the commander of United States Forces Korea, warned of Pyongyang's "growing cyber warfare capability."
The secretive regime "employs sophisticated computer hackers trained to launch cyber-infiltration and cyber-attacks" against South Korea and the United States, Thurman said in a statement before the U.S. House Armed Services Committee.
"Such attacks are ideal for North Korea, providing the regime a means to attack ROK and U.S. interests without attribution, and have been increasingly employed against a variety of targets including military, governmental, educational and commercial institutions," he said. ROK is short for Republic of Korea, South Korea's official name.
Tensions have flared recently on the Korean Peninsula after the North carried out its third underground nuclear test last month.
The United Nations Security Council responded by stepping up sanctions on the regime in Pyongyang, a move that prompted a fresh barrage of bombastic threats in North Korean state media.
CNN's K.J. Kwon reported from Seoul, and Jethro Mullen reported and wrote from Hong Kong. Judy Kwon and Hilary Whiteman in Hong Kong contributed to this report.