> JapanHacked_
[Investigating][Severity: Major][Intrusion]

Yomisen WEST: unauthorized access to the Shikoku branch's Yomipost site

On 26 October, the advertising firm Yomisen said the website of Yomipost, a posting service run by the Shikoku branch of group firm Yomisen WEST, was accessed without authorization, and addresses, names, genders, phone numbers and email addresses of about 1,700 people may have leaked. It was found on 14 October and reported to the Personal Information Protection Commission on 16 October. The site has been closed and will be merged into Yomisen WEST's site.

Disclosed

2026-10-26

Organizations involved

1

Leaked or at risk

1.7K

1,700

Downtime

Unknown

Timeline

  1. Detected 2026-10-14
  2. Disclosed 2026-10-26
  3. 12 days

Attack or cause

Method
[Intrusion]
Impact
[Data leak]
Entry point
Web app

Data exposed or at risk

[Name][Gender][Postal address][Phone number][E-mail address]

Services hit

Organizations involved

Open in organization search

Sources

  1. [1][Official]読宣WEST四国支社ウェブサイトへの不正アクセスによる個人情報流出の可能性に関するお詫びとお知らせYomisen · 2026-10-26
  2. [2][News]読宣WEST四国支社に不正アクセス　1700人の個人情報流出Nikkei · 2026-10-26