It is unclear who was responsible for a massive cyber attack on major broadcasters and banks in South Korea on Wednesday, but authorities say there is a strong chance that North Korea was behind it.

Government officials here believe no individual hacker could have launched such a major attack, and the modus operandi points to the North. North Korea launched so-called denial of service attacks in 2009 and 2011 aimed at major South Korean websites.

Major North Korean websites including the state-run Rodong Sinmun daily and broadcaster KCNA apparently suffered connection failures on March 13 and 14 after being hit by a hacking attack. A key government official here confirmed that the North was indeed hit by a cyber attack but the source was unknown.

The Rodong Sinmun threatened in an editorial last Friday that the North would not stand by and suffer what it referred to as "dirty" acts.

Wednesday's hacking attack came just five days after North Korea's threat. "The cyber attacks against North Korea could have been fabricated by the North itself to justify its latest provocation," said Ryu Dong-ryeol of the Police Science Institute.

It also occurred just as joint South Korea-U.S. military drills draw to a close. "The sinking of the Navy corvette Cheonan in 2010 happened on the last day of joint drills," said Cho Young-ki of Korea University. "It's been North Korea's long-time tactic to catch us off guard by launching provocations when the level of alertness is reduced."

The government and military believe North Korea has an edge over the South in cyber warfare.

South Korean intelligence say North Korea has more than 30,000 cyber warfare specialists whose capabilities rival those of the CIA. The government says South Korea suffers 250 million hacking attempts every day, most of them originating in North Korea. The government has responded by coordinating with the military and National Intelligence Service's National Cyber Security Center, which acts as the shield protecting 4,000 government agencies against cyber attack.

The NIS has about 1,800 kinds of hacking detection technologies, but they are not enough, experts say, to stem the ever-evolving forms of hacking.