[Contained][Severity: Critical][Ransomware]

Matsuzawa Shoten: ransomware attack

Matsuzawa Shoten, a wholesaler of sheet music and music books, disclosed on 9 May that its servers were accessed from outside and infected with ransomware. Its ordering systems stopped, including the Gakufu Navi and Chumon-kun services for retailers. Ordering from publishers and makers was restored on 18 May, and Gakufu Navi and Chumon-kun are coming back feature by feature.

Disclosed

2026-05-09

Organizations involved

Leaked or at risk

Unknown

Downtime

Unknown

Timeline

Disclosed 2026-05-09
1 days

Attack or cause

Method: [Ransomware]
Impact: [Service outage]
Entry point: Unknown

Data exposed or at risk

–

Services hit

Service	Role	Impact level	Note
Chumon-kun	[Breached]	[Critical]
Gakufu Navi	[Breached]	[Critical]

Organizations involved

[Breached][Critical]Tokyo, ItabashiWholesale and retail trade
Matsuzawa Shoten Inc.

						Note
Matsuzawa Shoten Inc.	[Breached]	[Critical]	Tokyo, Itabashi	Wholesale and retail trade	Unknown

Open in organization search

Sources

[1][Official]【お取引先出版社様へ】弊社受発注システム障害（ランサムウェア感染）に関する進捗状況のご報告（５月２７日８時時点）Matsuzawa Shoten · 2026-05-27