Company

Gakken Holdings

Gakken Holdings (Shinagawa, Tokyo; Education and learning support) appears in 1 related cybersecurity incident. The latest was disclosed on 2026-10-29.

Profile

Industry/type: Education and learning support
Location: Tokyo, Shinagawa
Listing: TSE Prime 9470
Website: https://www.gakken.co.jp/

Public figures

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Metric	Value	Scope	As of	Source
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Incident history

Disclosed 2026-10-29Updated 2026-11-05 22:59Aichi, Akita, Chiba, Fukui, Fukuoka, Fukushima, Gifu, Gunma, Hokkaido, Hyogo, Ibaraki, Iwate, Kagawa, Kagoshima, Kanagawa, Kochi, Kyoto, Mie, Miyagi, Miyazaki, Nagano, Nagasaki, Niigata, Okayama, Okinawa, Osaka, Saga, Saitama, Shiga, Shizuoka, Tochigi, Tokushima, Tokyo, Toyama, Yamaguchi, Yamanashi[Investigating][Severity: Critical][Through a supplier][Major]
Arara: Arara Message breach exposes about 77 million email addresses; count under review
[Web app exploit][Data leak][Service outage]Leaked 77MOrganizations 380

		Incident	Role	Impact level				Methods	Impacts		Status
2026-10-29	2026-11-05 22:59	Arara: Arara Message breach exposes about 77 million email addresses; count under review	[Through a supplier]	[Major]	[Critical]	380 Sumitomo Mitsui Banking Corporation, Internet Initiative Japan Inc., Mitsui Fudosan Co., Ltd., Mos Food Services, Inc., Yamanashi Prefecture, AIRDO Co., Ltd., Arara Inc., Asoview Inc., Avance System Co., Ltd., Belc Co., Ltd., Camel Coffee Co., Ltd., Chobirich Inc., DATA X, Inc., Duskin Co., Ltd., GMO Payment Service Inc., Hokuriku Electric Power Company, HR Solutions, Inventit, Japan Leisure Channel Co., Ltd., Java Corporation, Jupiter Golf Network Co., Ltd., Kakaku.com, Inc., Kintetsu Miyako Hotels Inc., Maker's Shirt Kamakura, Martial Arts Legal Professional Corporation, Matsui Securities Co., Ltd., Monteroza Co., Ltd., NTT TownPage, ODK Solutions, Sasebo City, Seijo Ishii Co., Ltd., Shochiku Multiplex Theatres Inc., Solaseed Air Inc., St. Cousair Co., Ltd., Sumitomo Realty & Development Co., Ltd., Takii, TKC Corporation, U Co-op, Workman Co., Ltd., Zaif Inc., Ministry of Internal Affairs and Communications, City of Yokohama, Fukuoka City, Kawasaki City, Kyushu Railway Company, Okayama Prefecture, Okinawa Prefectural Government, Osaka City, Osaka Prefectural Government, Osaka Prefectural Police, Shiga Prefecture, Suzuki Motor Corporation, Daito City, Fuji Television Network, Inc., Fukui Prefecture, Fukushima City, Himeji City, Human Academy Co., Ltd., Isahaya City, Iwata City, The Kagoshima Bank, Ltd., Karatsu City, Kinko's Japan Co., Ltd., Koriyama City, Kumagaya City, Marugame City, Matsudo City, Miyazaki City, Naha City, Nasushiobara City, Nishinomiya City, Odawara City, Okazaki City, Otsu City, Shimonoseki City, Suzuka City, Takatsuki City, Toda City, Toyohashi City, Utsunomiya City, Yao City, Aikawa Town, AKASE GROUP Co., Ltd., Akita City, Albait Times Co., Ltd., Asahi Mutual Life Insurance Company, Aya Town, Bank of the Ryukyus, Limited, Barnes de Stroes Japan Limited, BEENOS Entertainment Inc., Bic Camera Inc., BOATRACE Promotion Association, Co-op Aichi, Co-op Gifu, Co-op Mie, Congrès Inc., Densan Co., Ltd., DH Inc., e-CHANNEL Co., Ltd., Echizen Mikuni Boat Race Authority, Ekitan & Co., Ltd., Fanplus, Fire Equipment and Safety Center of Japan, Fujiidera City, Fujinomiya City, Fukui Shimbun Co., Ltd., Fukuoka Chikagai Kaihatsu Co., Ltd., Gakken Holdings, GMO Epsilon, Gold Flag Co., Ltd., Granvista Hotels & Resorts, Hakone Town, Hamanako Boat Race Authority, Hasegawa Co., Ltd., Higashikurume City, Higashimurayama Regional Promotion Organization, Hinode Publishing Co., Ltd., Honjo City, Human Resocia, ILL, Itako City, Itami City, its communications Inc., Iwamizawa City, Iwate Prefectural University, Japan Digital Laboratory, Joseikan Co., Ltd., Kagoshima Shinkin Bank, Kagoshima Sogo Shinkin Bank, Kaisei Town, Kameyama City, Kanagawa Municipal Information System Association, Kasama City, Kashiwazaki City, Kintetsu Real Estate Co., Ltd., Kitamoto City, Kiyosu City, Kobe Shimbun Inc., Kojima Co., Ltd., Kotsu Shimbunsha, Kracie Pharmaceutical, Ltd., Kurihara City, Lee Mills & Company Co., Ltd., LightUp Shopping Club Inc., M.STAGE Co., Ltd., M.STAGE Management Solutions Co., Ltd., Manazuru Town, Matsuda Town, Medicus Shuppan, Publishers Co., Ltd., Mibu Town, The Minami-Nippon Bank, Ltd., Minkabu The Infonoid, Misato Town (Saitama), Miyoshi Town, Motegi Town, Musashimurayama City, Nagakute City, Nakai Town, Naruto City, Natural Island Co., Ltd., Natural Science Co., Ltd., Nihon Fukushi University, Ninomiya Town, Nishitetsu Hotels Co., Ltd., Nishitokyo City, Nishiwaki City, Nyuzen Town, Odakyu Travel Inc., Officemotion Co., Ltd., Oi Town, Oiso Town, Ome City, Osaka Gas Co., Ltd., Paris Miki Asset Management Co., Ltd., Rakuten Securities, Inc., Ryobi Holdings Co., Ltd., Saito City, Sakai City, Samantha Thavasa Japan Limited, Sanjo City, Sano City, Setagaya Shopping District Promotion Association Federation, Shimotsuke city, Shioya Town, Sodegaura City, Sofmap Co., Ltd., Taka Town, Takanezawa town, Tama Shinkin Bank, Ticketplus, Inc., The Tochigi Bank, Ltd., Toho Cash and Carry, Tomakomai City, Toyoake City, Tribeck Inc., Tsunagu Group Holdings, Vendome Yamada Co., Ltd., WATAMI FAST CASUAL MANAGEMENT Co., Ltd., WingArc NEX Inc., Yaita City, The Yokohama Rubber Co., Ltd., Yokoshibahikari Town, Yugawara Town, Nagareyama City, Niigata City, AUTHENTIC JAPAN Co., Ltd., Japan Society of Civil Engineers, The Nikkan Kogyo Shimbun, Ltd., Shiki City, Tokyo Kantei, Umanity Inc., Will Co., Ltd., Kawaguchi City, Itabashi Shopping Street Promotion Association Federation, JERA Co., Inc., Maniwa City	Aichi, Akita, Chiba, Fukui, Fukuoka, Fukushima, Gifu, Gunma, Hokkaido, Hyogo, Ibaraki, Iwate, Kagawa, Kagoshima, Kanagawa, Kochi, Kyoto, Mie, Miyagi, Miyazaki, Nagano, Nagasaki, Niigata, Okayama, Okinawa, Osaka, Saga, Saitama, Shiga, Shizuoka, Tochigi, Tokushima, Tokyo, Toyama, Yamaguchi, Yamanashi	[Web app exploit]	[Data leak][Service outage]	77,000,000	[Investigating]