2ch Chronicle/Deanonymization Incident
On August 26, 2013, personal information (including credit card data) was leaked from 2channel Viewer, 2ch's premium membership service. This led to the embarassing deanonymization of various individuals, as well as exposing them to identity theft. The crisis rocked the Japanese Internet, and many major celebrities, bloggers, and typical normal users had their scandalous post history uncovered.
To raise funds, 2channel had a premium 2channel Viewer service, which provided extra services, made the freshest thread archives available, and gave users access to the popular News4VIP (a random board akin to /b/). 2channel processed and stored all credit cards themselves rather than relying on a secure third party payment system. 2channel predated the popularization of PayPal and it's clones, and the administration probably held a desire to keep user data out of the hands of contractors, who would be vulnerable to Japanese government subpoena.
Unfortunately, on August 26, 2013, a poster named `さっしーえっち MwKdCUj7XWlQ` anonymously uploaded leaked full name, address, phone number, email address, and credit card information from 2channel Viewer to Onion (Onion Channel) via the Tor Network.
This crippling security breach unleashed waves of lawsuits against 2channel, a loss of confidence in the treasured anonymity of the website, and the wholesale destruction of 2ch's longtime dedicated userbase. While credit cards could be cancelled, identities could not be unleaked.
The first revelation was the discovery that some Matome blogs were actually manufacturing drama during slow news days.
Another bombshell revelation was that 2channel's staff had to collect complete user data and tripcodes (for comment history) of it's core userbase for tax purposes, which was beyond ordinary IP logs. This ended the thin veneer of anonymity on the site, and it's most prolific commenters would never dare approach the community again.
The most important effect was the loss of a stable source of income for 2channel. As a result, 2channel would undergo strange behavior to stay afloat.