The 'Gyeongin Daecheop(Metal Tiger Great Victory)' (경인대첩(庚寅大捷))¹⁾ was the civilian-led cyberwarfare campaign between Japanese and South Korean internet communities which occurred in the month of March 2010. For the losing side, it became known as the 'March 1st F5 Attack' (三・一F5アタック).

In retaliation for inappropriate Japanese commentary on 2channel, regarding the Korean exchange students attacked by Russians in Barnaul^2)3)4)5) and Yuna Kim's success in the 2010 Winter Olympics,⁶⁾ several Korean internet communities would unite with the goal of launching an attack on 2channel, setting up bases to organized their attack on websites like DC Inside and Naver on February 24, 2010.⁷⁾

Of course, somebody ended up warning 2channel about the imminent attack planned for March 1, 2010, the March 1st Movement's anniversary,⁸⁾ so both sides tightened up security. When Yuna Kim won gold, a Japanese false-flag attack was conducted on 2channel's “Yaoi” (/801/) board⁹⁾ to escalate said situation, but the Koreans were busy celebrating and the attacks on DC Inside didn't do much.

After studying the weapons used against 2channel, the Korean programmers unleashed 'KPS2'¹⁰⁾ and 'UDP Flooder' on the day of the attack. In short, the Koreans had a massive advantage as this was a weekday. Despite efforts to mitigate the damage, every server went down by 5:00pm,¹¹⁾¹²⁾ so 2channel's management surrendered, the Japanese surrendered at 8:43pm, and the Koreans declared victory at 9:38pm.

Following the war and light skirmishes that followed,¹³⁾ both sides have speculated if the conflict would reignite since Japan and South Korea are in a number of disputes and organized boycotts. However, it has been said that the war was unique as it reflected what the internet was like back then, as DDoS attacks and raids used to be fairly common, so it would be rare if either side resorted to these tactics today.

• Japan and South Korea both used UTC+09:00 in 2010, with neither party observing DST.
• When the plan leaked, Naver added a membership question and DC Inside added a rather intimidating CAPTCHA to deter spies whose answer was reference to a then-viral Nongshim commercial.¹⁴⁾
• NTTEC (PIE), the company that maintained 2channel's servers, initially described their campaign as a “primitive F5 reload attack” (原始的なF5リロード攻撃).¹⁵⁾ After the servers went down, they changed the story to a “mass amount of bot computers”, and claimed that all of the documented information were forwarded to the “local authorities”¹⁶⁾ around March 2, 2010 at 12:03am.¹⁷⁾¹⁸⁾
  • Japanese media would spread rumors that the FBI was involved and estimated $2.5 million USD in damages,¹⁹⁾²⁰⁾ but this issue is that the estimate came out way too quick and the FBI probably wouldn't get involved as it wasn't directly targeting a U.S. entity. Theoretically, this issue should have been raised to the CIA, in cooperation with South Korea's NIS and Japan's CIRO.
• On March 2, 2010, it was reported that the ROK Air Force had crashed two F-5 jets.²¹⁾²²⁾ Some Japanese nationalists may claim that this war ended in a 'tie' despite having zero involvement.
• There were plenty of Japanese text artwork involving Nida, but most of these offer an extremely biased side of events with the “F5 attack” narrative, so I've opted not to display them in this article.
• Sankaku Complex is not a news source. The website mostly echoed the Japanese perspective by framing Koreans as nationalists (omitting the Barnaul attacks),²³⁾ echoing a damage estimate from the right-wing Sankei Shimbun,²⁴⁾ then they suddenly defend “freedom of speech” out of nowhere.²⁵⁾
• By coincidence, 2010 was the 100th anniversary of the controversial Japan–Korea Treaty of 1910, where Imperial Japan arguably coerced the annexation of the Korean Empire.

• 2010 Japan–South Korea cyber conflict on Wikipedia [EN]
• 2010 March 1st Cyber War on Namu Wiki [KO]
• March 1st F5 Attack on Niconico Encyclopedia [JA] - Warning for extremely transparent racism.