Incident
Ross Ulbricht ran the Silk Road darknet market from 2011 to 2013 under the handle "Dread Pirate Roberts." He was arrested in October 2013 and sentenced to life in prison.
What happened
In January 2011, days after Silk Road launched, a user named altoid posted on the Shroomery mushroom forum and on Bitcointalk, casually "asking" about this new site, early-stage marketing posing as word of mouth. Eight months later, the same altoid account posted a job listing on Bitcointalk for a "venture-backed bitcoin startup," telling applicants to contact rossulbricht@gmail.com.
In 2013, IRS investigator Gary Alford ran targeted Google searches for the earliest mentions of Silk Road, found the altoid posts, and connected the account to the Gmail address. Records for the Google account narrowed the investigation to San Francisco, where subsequent surveillance and forensic work confirmed the identification. Ulbricht was arrested in a public library with his laptop open and logged into the site's admin panel.
The OPSEC mistake
One account bridged two lives. The altoid handle belonged to the anonymous project; the Gmail address belonged to the real person; a single post connected them, permanently and publicly. Everything that followed (millions in security spending, Tor, encrypted servers) could not undo one forum post from before the operation mattered.
Why it mattered
Anonymity failures are retroactive. The post sat in public view for two years; it only needed to be found once. Early-stage sloppiness, from before a project seems worth protecting, is indexed, archived, and waiting.
How it could have been avoided
Strict separation from day one: the identity that promotes a project must share nothing (no handles, no email addresses, no writing quirks) with the person behind it. And identities cannot be retrofitted: by the time something is worth protecting, its history already exists.
Defensive lesson
Whatever you may someday want unlinked from you, a pseudonymous blog, an activist account, a business venture, build the separation before the first post, not after the project succeeds. Old posts don't expire; search only gets better. See Identity Compartmentalization.